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DENVER — Two partisans, locked in a tight race to win over moderate voters in this purple state, sparred for nearly an hour Monday morning over their respective records in Washington.

Democratic Sen. Mark Udall defended his support for Obamacare and underscored his support for a tax on carbon pollution, while criticizing Republican Congressman Cory Gardner’s voting record as being “out of the mainstream.”

Gardner, who looked to soften his positions on issues like immigration and climate change, sought to portray Udall as a loyal foot-soldier for President Obama, who he quoted repeatedly throughout the Denver Metro Chamber of Commerce debate co-sponsored by POLITICO and FOX31 Denver.

“The president said it the other day: His policies are on the ballot,” Gardner said. “If we elect Mark Udall, who’s voted 99 percent of the time for these policies, what makes us think anything’s going to be different than it’s been the last six years?”

Udall, in his closing statement, mocked Gardner’s tag-line from his TV ads that he’s representative of the next generation.

“Congressman Gardner talks about being part of the next generation, a new Republican,” Udall said. “Well, the next generation doesn’t want to shut off science, the next generation doesn’t want to shut out immigrants, the next generation doesn’t want to shut down government.

“The next generation — all generations, frankly, see the world my way,” Udall continued, in a statement GOP operatives were quick to mock as they left the Seawell Ballroom following the debate.

Gardner attempted to soften his stance on some of those issues, after being pressed by moderator Manu Raju, senior congressional reporter for POLITICO, on whether he supports a path to citizenship for undocumented immigrants, which was part of the Senate immigration overhaul passed last June that House Republicans refused to take up.

“I believe a path to earned status is going to be part of the solution,” Gardner said twice in response to Raju’s question, stopping short of stating explicitly that he supports a path to actual citizenship.

He took a similar tack when pressed on whether he believes climate change is human-caused, which he’s mostly denied until now.

“There is no doubt that pollution is causing climate change,” Gardner said.

Gardner put Udall on the defensive over the Democrat’s support for cap and trade policies, which he reaffirmed his support for Sunday on FOX31 Denver’s #COpolitics: From The Source.

“I support putting a tax on carbon,” Udall told Raju, before Gardner chimed in with his own question.

“What is the price you would put on carbon?” Gardner asked.

Udall opted not to answer that question, stating instead that Colorado is ready to innovate and tackle the problem of climate change.

Republicans argue that a carbon tax would have a negative impact on the economy.

Udall offered a stronger defense of the Affordable Care Act than he did in the Club 20 debate a month ago, touting the early positive returns — 400,000 people purchasing plans on Colorado’s insurance exchange, premiums increasing an average of just 2 percent this year and the state’s uninsured rate dropping from 17 percent to 11 percent — while affirming that he would vote for Obamacare again.

Gardner focused on the 340,000 Coloradans who received cancellation letters and argued that there are 2.5 million fewer workers because of the law.

Gardner also brought up an old attack against Udall that his vote for Obamacare resulted in a $800 million cut to Medicare, seeming to trap Udall in an effort to set the record straight and explain that the cuts Gardner referenced are actually reductions to future spending.

“Congressman Gardner voted for $800 billion in cuts to Medicare that went to tax cuts,” said Udall. “I voted for $800 billion in cuts to Medicare Advantage that went to shoring up Medicare and extending the solvency of it.”

Republicans left the room giddy over the fact that Udall strung together the phrase “I voted for $800 billion in cuts to Medicare”, which may be cut and pasted into a forthcoming GOP attack ad, as Bloomberg Politics’ Dave Weigel predicts.

“In this case, Udall made a classic Kinsley gaffe, saying something true in a manner that can be weaponized against him,” Weigel wrote following the debate.