WASHINGTON — The Senate is closing in on a health care bill that could affect coverage for tens of millions of Americans and overhaul an industry that makes up one-sixth of the economy.

Only one problem: Almost no one knows what’s in it.

"I think it's being written, uh, by someone somewhere but I'm not aware of who or where," Sen. Rand Paul, R-Kentucky, deadpanned to NBC News. "If you get a copy of it, will you send me a copy?"

In a striking break from how Congress normally crafts legislation, including Obamacare, the Senate is conducting its negotiations behind closed doors. The process began five weeks ago, after the House passed its version of health care reform, with a small working group of 13 senators rather than the broader committees who usually handle the issue.

The opaque process makes it impossible to evaluate whether there are any significant changes coming to health care. There are no hearings with health experts, industry leaders, and patient advocacy groups to weigh in where the public can watch their testimony or where Democrats can offer amendments.

“We'll let you see the bill when we finally release it,” Senate Majority Leader Mitch McConnell (R-KY) told reporters on Tuesday. He added that “nobody is hiding the ball here” and that people were “free to ask anybody anything.”

Free to ask, but answers are another matter. Republican senators are still negotiating over specific pieces of a bill, but they say they’re close enough to producing legislation that they could hold a vote within weeks. They have been tight-lipped on the details, leaving Americans with only a trickle of leaked ideas that are often vague or speculative.

Health and Human Services Secretary Tom Price said in a hearing on Thursday that his staff had provided "technical assistance" to senators working on the bill, but that he had not seen any "legislative language" himself.

Democrats have complained about being shut out, but even some Republican senators have said they’ve had difficulty getting information about the legislation and wished there were more public opportunities to register concerns.

"Would I have preferred a more open process? The answer is yes,” Sen. Bill Cassidy (R-La.) told reporters on Monday evening.

Sen. Bob Corker (R-Tenn.) said that he’s complained to leadership about the lack of transparency. “I would have liked to have seen a public process — get buy-in from the public,” he said. “I’ve said that in several of our meetings but that’s obviously not what’s going to happen. Now when the bill’s complete, the public then will have a chance to view it.”

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Asked if they had seen any legislative text, a Republican aide to a member of the 13-person Senate working group deadpanned: “Why would they show us any legislation?"

The approach is broadly similar to the process that produced the American Health Care Act in the House last month. At the time, leaders released a finished bill and voted on it within 24 hours — so fast that the Congressional Budget Office couldn’t estimate its cost and effects for another three weeks. The move was a jarring shift after years of promises from House GOP leaders to slow down major legislation and post all bills online several days before a vote.

Democrats are increasingly drawing attention to the lack of transparency, which they’ve criticized as an effort to rush through legislation before Americans can scrutinize its effects or individual lawmakers can push for changes.

“Will we have a hearing on the health care proposal?” Sen. Claire McCaskill (D-Mo.) pressed Finance Chairing Sen. Orrin Hatch (R-Utah) in a separate hearing last week. Hatch would not commit to one, but invited McCaskill to pass on her ideas. “We have no idea what’s being proposed,” McCaskill responded.

On Tuesday, several Democratic members linked the closed process to a change in the Senate’s media policy that blocked reporters from filming in the hallways.

“Why are they doing that?” Minority Leader Chuck Schumer (D-N.Y.) said at a weekly press conference. “It's obvious. They don't want the American people to see how poorly they would do under this bill.”

It was not clear there was a connection, however: After blowback, Republicans expressed surprise at the shift and Rules Committee Chairman Sen. Richard Shelby (R-Ala.) said no new restrictions had been approved.

During the crafting of the Affordable Care Act, Republicans complained about a lack of transparency on the bill that reformed the health care system. Then-House Speaker John Boehner gave a fiery floor speech, saying just before the House vote on Obamacare, “Read the damn bill before you vote.”

But Senate Democrats spent months in 2009 negotiating different versions of a health bill through multiple committees in the House and Senate. The committees then spent days on markups in which members could offer amendments and the full Senate held an open debate on the final version for 25 days. After the House passed the Senate bill in March, they made a series of tweaks using the budget reconciliation process, which Republicans are using exclusively to pass their own bill.

“What’s going on here is backwards,” John McDonough, a professor of public health at Harvard who was a Democratic Senate aide during the ACA debate, told NBC News. “The attempt to keep it in the dark is to make sure that as few Americans as possible know what’s in it and what the implications of it are,” he added.

Sen. John Barrasso (R-Wyo.), a member of the Senate leadership team, defended the process on Tuesday, saying Democrats would have an opportunity to offer amendments once the bill was put on the floor. Pressed on the lack of committee hearings or input by a reporter, he described the Senate GOP working group as “a committee of the whole.”

Critics see the gambit as a response to the House bill’s poor reception after the CBO estimated it would leave 23 million fewer people insured, while raising premiums and deductibles for many low-income and older Americans. A Kaiser Health tracking poll in May found 55 percent of respondents have an unfavorable view of the House bill versus 31 percent who view it favorably, and most polls have found a similarly negative reaction.

Asked whether Republicans were operating from the assumption any bill they passed would be unpopular, Barrasso suggested he wasn’t concerned about pleasing their loudest critics.

“There is nothing that I think that the Senate can pass that is going to satisfy the left activists in California [whose] state senators have just voted for a single payer plan,” he said.

There are some factors that could slow down the Senate. In comparison to the House, the Senate is barred from voting on a bill before a cost and impact estimate is released from the nonpartisan CBO.

But if the Senate is to really vote before they leave town for a week on June 30th, a goal that many Republicans hope is still achievable, that leaves little time for the public to see legislation. A CBO score takes 10 to 14 days to produce. There are only 17 days left before the end of the month.