Vice President Joe Biden has some nice things to say about Democratic presidential candidate Bernie Sanders, especially when it comes to understanding issues that are important to Democrats.

"Bernie is speaking to a yearning that is deep and real. And he has credibility on it," the vice president said on CNN Monday, referring to the issue of income inequality.

He said that former Secretary of State Hillary Clinton has "come forward with some really thoughtful approaches" to tackle that subject, but that it's "relatively new" for her to talk about.

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"Hillary's focus has been other things up to now, and that's been Bernie's -- no one questions Bernie's authenticity on those issues," he said.

Biden's comments come as the race between Clinton and Sanders heats up. A new poll out Sunday showed the Vermont senator in a virtual tie with Clinton in the Hawkeye State. The NBC/Wall Street Journal/Marist survey showed that among likely Iowa Democratic caucus-goers, Clinton edges out the Vermont senator by just three points, 48 percent to 45 percent -- a lead within the poll's margin of error of 4.8 percentage points.

Clinton has honed in on Sanders' past positions on guns, repeatedly criticizing his vote in favor of 2005 law that absolved gun manufacturers of any legal liability when someone uses their products during the commission of a crime. Sanders has defended the vote by pointing to the fact that he represents a state with a strong hunting tradition where, as recently as 2010, over half of adults owned guns.

But Biden defended Sanders on the issue in the CNN interview.

"What Bernie Sanders has to do is say that the Second Amendment says...you can limit who can own a gun, that people who are criminals shouldn't have guns," he said. "People who are schizophrenic and have mental illnesses shouldn't own guns. And he has said that."

On Tuesday, Biden cast doubt on whether a Democrat will win the 2016 election.

"Yes, I think it's possible,'' he said on "The Today Show" when asked whether he could imagine businessman Donald Trump winning the presidency in 2016.

"I hope that if that were to occur -- I hope it doesn't because I have fundamentally different views than he does -- I'd hope that he gets a lot more serious about the issues, a lot more serious about gaining knowledge about this this nation functions and foreign policy and domestic policy, but look, that's a long way off."

Biden was considering running for the Democratic nomination, but announced in October that he would not run, citing the length of time his family needed to grieve after his son, Beau Biden, died of brain cancer in May. He said last week of the decision, "I regret it every day, but it was the right decision for my family and for me."