[John King, Cnn Anchor:] Good evening from the CNN Election Center. I'm John King. Two important stories we're tracking this hour. The Taliban vowed beheadings of Americans to retaliate for the massacre of Afghan civilians allegedly at the hands of an Army staff sergeant. And the horrific violence raises new questions about the decade-long U.S. military mission and about the care given soldiers with traumatic brain injuries. Plus, the Deep South gets its say in the roller-coaster Republican presidential race. Will Alabama and Mississippi cement Mitt Romney as the front-runner or help Newt Gingrich engineer yet another comeback? Let's begin with the latest round of voting. Four contests in all tonight. Hawaii and American Samoa also casting ballots, but most of the attention is focused on Alabama and Mississippi. Late polls in both states showed races too close to call. Our exit polls also suggest a fierce competition in both states with conservative support. Let's look at some of the early exit polling, we will bring this over for you. Here we are in the state of Mississippi tonight. Voters were asked as they went to the polls what's the most important candidate quality. You can see more than four in 10 Republican voters in the state of Mississippi today say their number one priority is beating President Obama in November. About 20 percent say they want a true conservative. About 20 percent say strong moral character matters most to them. Let's move over and look at the state of Alabama. Same question. What's the most important candidate quality? Little lower number there, but about four in 10 say the most important thing they want is a candidate who can defeat President Obama. A true conservative, strong moral character and the right experience about equal, right around 20 percent, a little below that right there. Let's move again to the next question here, who is that candidate? Remember this is not telling you who they voted for. Voters are asked regardless of who you voted for, who do you think would be the strongest candidate against President Obama? Governor Romney, the former governor of Massachusetts, 52 percent of Mississippi voters said they believe Romney would be the strongest candidate. Again that doesn't mean that's who they voted for but that's what they think. In the state of Alabama, Romney came out on top 46 percent of Republicans there said he was the candidate they believe most likely defeat Obama. Again, doesn't mean who they voted for 23 percent said that of Speaker Gingrich, 24 percent of Senator Santorum. One last question from the exit polls, are Romney's positions on the issues too conservative, not conservative enough or about right? Well, in the state of Mississippi, more than half of the voters today said his positions are not conservative enough. Remember, this is a conservative Southern state. And in Alabama, a higher number, 55 percent said Governor Romney's positions are not conservative enough. So where did these voters go? Let's take a closer look on this one 42 percent of Alabama voters who said Romney's not conservative enough voted for Rick Santorum 40 percent of those who said Governor Romney's not conservative enough voted for Speaker Gingrich. It shows you not only a fierce competition for the most conservative voters, but potentially a split among conservative voters that conceivably in the end actually could help Governor Romney. We will watch how that plays out as we actually get the results. The stakes tonight are enormous. A win by Governor Romney in the South would significantly bolster his front-runner credentials. And many Republicans argue Gingrich needs a Southern sweep to keep his bid alive. Let's get a first impression from Candy Crowley, Gloria Borger, and David Gergen. For Governor Romney, this is about proving you're a real Republican in the geographic base of the party. If he wins one, is it over?
[Candy Crowley, Cnn Senior Political Correspondent:] I think so. I think if he answers that question listen, whoever thinks that those folks who are going to vote for Santorum or Gingrich tonight will turn around and vote for Obama in the fall, crazy. Let's put that out on the table. But, yes, I think when you look at Mitt Romney has the most to win out of tonight and Newt Gingrich has the most to lose. And Santorum goes on.
[King:] Santorum goes on regardless?
[Gloria Borger, Cnn Senior Political Analyst:] Yes, I think Santorum continues. His campaign will tell you that they have got some good primaries coming up. They can do Pennsylvania, that this isn't a math problem. But I think the party has a head-heart problem. If you look at the numbers you just showed, their heads are telling them electability. This is what we care about. But their hearts are saying Mitt Romney is not conservative enough. He doesn't share my values. So they're having a real tug-of-war there about who they want.
[David Gergen, Cnn Senior Political Analyst:] I think Rick Santorum has to win at least one of them to go on as a viable candidate. Anybody gets blanked out of both of these, if it's Newt Gingrich or Santorum...
[King:] It's hard to say that I'm a better conservative alternative to Mitt Romney if you lose two to him in the South, right?
[Gergen:] Exactly. Who thought we'd be here? Who thought Mitt Romney would be competitive at this point in these two states?
[King:] Is he competitive because he's competitive, Candy, or is he competitive because Gingrich and Santorum are still in the race splitting the vote?
[Crowley:] Yes, that's a big part of it. But we have also seen a lot of folks that have looked deeper into the numbers and who's your second choice. And it's not necessarily that if one of them gets out of the race all of those votes then go to the other. It doesn't work that cleanly.
[Borger:] Well, the Romney people say that if Newt Gingrich dropped out they'd get half of those that Santorum would get half of those votes. They'd only get 30 percent. But that 30 percent would be enough.
[Gergen:] But Santorum would also get if Newt Gingrich dropped out Santorum would start getting more money in. He would be a more competitive candidate. It would be a bigger test of Romney in the states ahead.
[King:] Conceivably, as we count the votes tonight, that's tomorrow's conversation. Either Gingrich or Santorum have such a bad night, it's time for them, even though they both insist, no, they're going on.
[Gergen:] If Romney wins one or both of these states, that's the other half of the conversation.
[King:] David, Gloria and Candy will be with us throughout the evening. It's an interesting night in Republican politics. And Alabama's conservative Republican governor made his preference known just this morning. Governor Bentley says he was voting for Rick Santorum. But the governor insists that's not a formal endorsement. Governor Bentley is live with us tonight from Montgomery, Alabama. Governor, explain the distinction for me. I assume that means you didn't call your political organization and say, get out there, turn out the vote, grab people by the ears and get them out for Senator Santorum? Am I right?
[Gov. Robert Bentley , Alabama:] Well, that's exactly right. I was asked last evening who I was going to vote for and I said I was going to vote for Senator Santorum. And that word got out today. And that that is the form of the endorsement. I actually believe it's not good to endorse people because people in this state like to make up their own mind. And I certainly believe they have the right to do that.
[King:] When you look at the voting, you just listened to the conservative we were having with our smart reporters and analysts here, you're a Santorum supporter. Do you think if Senator Speaker Gingrich should get out of the race or if Senator Santorum, say he comes in third or second and loses both these states, should one of the non-Romney candidates get out so that an allegedly more conservative alternative gets a one-on-one shot?
[Bentley:] You know, I don't think you should tell anybody to get out. I don't think it's anyone's right to tell a candidate to get out. they have been working hard on this campaign for a number of months and they certainly have a right to stay in as long as they wish.
[King:] What's your sense? You do see the head heart, as Gloria Borger just put it. A lot of Republicans say the most important thing is beating President Obama in the fall. And a lot of them then go on, in the next sentence, to say they think Governor Romney would be the strongest candidate. But then many of those same people are voting for somebody else, either Speaker Gingrich, Senator Santorum or Ron Paul. But what's the struggle of Republican voters right now that has extended this process and made it so unpredictable?
[Bentley:] Well, I think that any of the candidates would be good candidates. And I think that Governor Romney probably has the best chance of winning the nomination. I mean there's no doubt about that. But, you know, you should also vote your heart, I think. And if you believe that someone is the best candidate, even though you don't think they're going to win, I think you ought to vote for who you think is the best candidate.
[King:] You gave an interview to our former friend here at CNN, Bill Hemmer, on Fox News Channel yesterday, where you said you thought Governor Romney's Mormon faith would be a detriment to some voters in the state of Alabama. How significant do you think that is and does it bother you, sir?
[Bentley:] You know, it really does not. It does not bother me. But I don't think that it is it is a very subtle thing. And and no one is going when you question people, most people will not admit that. But I I do think, not just in Alabama, but I think in many non-Mormon states, I think it certainly can be a a problem for in the primary, in the primary. But now once the general election comes around, if Governor Romney is the nominee, it will not be a problem.
[King:] I assume Alabama will stay red in November. Governor Bentley, we certainly appreciate your time tonight, sir. A fascinating night. We'll watch as the results come in, along with you.
[Bentley:] Thank you.
[King:] Thank you, sir. Now let's shift to today's major international news, the fallout from the massacre of Afghan civilians allegedly by an Army staff sergeant who'd been treated for a traumatic brain injury after an earlier tour in Iraq. Two senior military officials now telling CNN alcohol was found in an area of the base where the suspect lived. And they're investigating now whether alcohol might have been a factor in the rampage. But they also caution us the alcohol may not have belonged to the suspect at all. Also, military officials say the military now reviewing pictures of the soldier leaving the base and then returning later. In eastern Afghanistan today, about 500 people blocked a highway, burned effigies and shouted anti-U.S. slogans, but their demonstrations stayed peaceful. The Taliban, however, promised bloody retaliation, is now threatening to behead Americans. But at both the White House and on the campaign trail, we're hearing calls for the United States to stand firm and resist the temptation for any quick changes in policy. Here's what Republican candidate Mitt Romney told CNN's Wolf Blitzer just moments ago.
[Mitt Romney , Presidential Candidate:] It's certainly time on a regular basis to review our mission there and to see what progress we're making, and not to make decisions based upon some actions by a crazed gunman. We don't determine our foreign policy based on something of that nature.
[King:] At the White House today, President Obama voiced his condolences for the victims and their families, but said the United States must complete its mission in Afghanistan.
[Barack Obama, President Of The United States:] There's no question that we face a difficult challenge in Afghanistan, but I am I'm confident that we can continue the work of meeting our objectives, protecting our country and responsibly bringing this war to a close.
[King:] Chief White House correspondent Jessica Yellin is here to take us inside the administration's deliberations. Jess, is there a chance, despite what the president says publicly, that this incident could become part of a pressure to move up the withdrawal date?
[Jessica Yellin, Cnn Chief White House Correspondent:] Well, John, it seems that way, but the White House is adamant that they have absolutely no intention of withdrawing troops sooner than the end of 2014, which, as you know, is what the president has publicly committed to. Now, privately we know there are disagreements within the administration about the rate at which those troops should be withdrawn. That's after the surge troops come out at the end of this summer. So senior military officials, they have made it known that they'd prefer as many troops stay as long in Afghanistan as possible. Now, some in the White House let's call it the Biden faction are believed to want to bring as many troops out as fast as possible. And then there are others prefer a middle option. Bottom line, publicly, the White House has committed to no timetable for that drawdown. All of that is to be announced.
[King:] And you say to be announced. Part of it is discussion with allies. The British prime minister, David Cameron, is here right now for conversations with the president. How important is Afghanistan to this meeting?
[Yellin:] Well, Prime Minister Cameron and President Obama are both major contributors to NATO forces. And NATO will be meeting in Chicago this May. Now, we expect this topic of troop drawdown in Afghanistan to be a topic of discussion there. And no doubt Prime Minister Cameron and the president would want to work something out to be on the same page or close to it in advance of that May NATO meeting. So, this seems an inevitable topic of conversation for these two men, John.
[King:] Our chief White House correspondent, Jessica Yellin. Jess, thanks. We will stay on top of this story. Another very important international story tonight, a former United Nations weapons inspector tells CNN Iran may have conducted explosive tests connected to a possible nuclear weapons program. David Albright, who is now the president for the Institute of Science and International Security, says his group has identified a building in an Iranian military base near Tehran as the possible site of a high-explosive test chamber. It's in the upper right quadrant of the picture you're seeing right there. Here's a closer view. Mr. Albright says the building has its own perimeter security, wall or fencing with an earthen berm separating it from a neighboring building. Very important qualities there for a building that could have a high-explosive testing facility. We will stay on track of that as well. And in just a moment, we will talk to Senator John McCain. He is being quoted today as saying the U.S. mission in Afghanistan is in jeopardy. We will also get more insights tonight on traumatic brain injury from one of the doctors who helped save the life of Congresswoman Gabrielle Giffords.