Heller passed up the opportunity to attack Berkley for the ongoing House Ethics Committee investigation against her, saying "the issue has essentially played itself out." 

That's a big shift from his attacks during the last debate and in an earlier statement, in which he said that Berkley is "the most unethical, corrupt person I've ever met in my life." It also follows months of campaign ads accusing Berkley of using her office to push for help for kidney doctors without disclosing her husband was one. 

Heller has led Berkley in most public polling of the state by a small margin, even as President Obama has led Romney in most of those polls. 

The debate follows recent weeks in which Heller has sought to tack to the center and put some distance between himself and the GOP nominee, most notably following Romney's remarks that 47 percent of the nation's voters see themselves as "victims" who are dependent on the government. 

Heller also sought the center on immigration, an important issue to the state's large and fast-growing Hispanic population. 

The Republican seemingly endorsed the DREAM Act, a bill he's previously voted against. At the debate, he said he'd support a path to citizenship for immigrants who entered the country illegally but are in the military or getting an education. 

"The principles that I'm trying to support is trying to make these people succeed," he said in defending his support of English-only education and calls for more legal immigration.

Berkley's campaign jumped on the "these people" phrase and has lined up a Friday morning conference call with Hispanic Democrats to hit Heller on it.

Heller also promised to work across the aisle to pass legislation to make online poker legal. He has come under criticism from Senate Majority Leader Harry ReidHarry Mason ReidWATCH: There is no Trump-Russia collusion and the media should stop pushing this The demise of debate in Congress ‘North by Northwest,’ the Carter Page remake MORE (D-Nev.), who has accused him of not doing enough to win GOP votes on the issue. 

"Twenty-six days from now, Sen. Reid and myself will put aside our differences and get something passed," he said. 

Berkeley, who argues the bill could create 1,200 jobs in Nevada, has seized on the issue.

“My opponent is failing the people of the state of Nevada,” she said at Thursday's debate. “My opponent is not doing his job. Either he does not have an understanding of how important this is to the state of Nevada, or he’s not caring.”

Rough weather interrupted the debate. As the two were fighting over energy policy, the power went out in the studio, leading Berkley to quip, "We could use some [energy] now," drawing laughs from the audience.