Beto O'Rourke needs to hit back.

It's tougher than it sounds.

His campaign against incumbent Sen. Ted Cruz has been defined by a positive message. He says Texans can come together to solve some of the nation's biggest challenges, like immigration policy, improving public education, criminal justice reform and affordable health care.

O'Rourke is a fundraising juggernaut, setting Texas records for money raised and spent by a federal candidate for office. And polls show he's within striking distance of pulling off the upset against Cruz in a statewide electorate that favors GOP candidates.

But there's reason for O'Rourke and his supporters to be concerned as Election Day approaches.

Cruz, the consummate alley fighter, has been throwing haymakers at O'Rourke, casting him as a liberal in the mode of Vermont Sen. Bernie Sanders and Massachusetts Sen. Elizabeth Warren. At their first debate in Dallas, Cruz accused O'Rourke of favoring the legalization of all drugs, including narcotics. In a move that would make a WWE villain/wrestler proud, Cruz suggested O'Rourke was a socialist after he was asked to say something positive about his rival. He basically hit O'Rourke with a chair in full view of the refs.

"True to form," O'Rourke said, an effective counterpunch.

He needs to do more of that.

Cruz knows that if Texas conservatives stick with him, he'll win the election. So he's trying to show conservatives that O'Rourke is too liberal for Texas. In doing so Cruz sometimes exaggerates O'Rourke's positions. For instance, the El Paso Democrat doesn't really want to legalize narcotics. He doesn't want open borders with drug cartels having the run of the country. He doesn't want to wreck the economy with a socialist health care law.

For the Oct. 16 debate in San Antonio, Cruz will again be on the attack, and O'Rourke must get better at protecting himself.

In politics it's dangerous to let attacks from rivals go unanswered. And even the most positive of candidates, like former Presidents Barack Obama and George W. Bush, ran relentless negative ads against opponents.

Former Massachusetts Gov. Mitt Romney never recovered from the onslaught of contrast ads Obama and Democrats put on him at the beginning of the 2012 presidential campaign.

One of Cruz's latest ads accuses O'Rourke of being "divisive, dangerous" and anti-law enforcement. It's a result of O'Rourke calling for an end to racial profiling by police officers.

"Now you have this Senate Democratic candidate saying, 'Maybe you're the bad guy,'" an anchor says in the commercial.

Cruz, first elected in 2012 and a 2016 presidential candidate, is not the most likable of politicians. He's had trouble with supporters of President Donald Trump that are angry because Cruz was slow to endorse his GOP rival. Then there are those who think Cruz has lost his dignity by cozying up to Trump, who has insulted him many times.

So far O'Rourke's response to Cruz has been a television ad. In it he states that voters should not be swayed by the negative attacks against him.

"We can be defined by our fears, or we can be known by our ambitions," O'Rourke said.

That's a nice start, but the next time Cruz goes negative, O'Rourke needs to smack him in the mouth.