Vice President Biden heaped praise on Hillary ClintonHillary Diane Rodham ClintonBiden slams Trump over golf gif hitting Clinton Overnight Cybersecurity: Equifax hit by earlier hack | What to know about Kaspersky controversy | Officials review EU-US privacy pact Overnight Tech: Equifax hit by earlier undisclosed hack | Facebook takes heat over Russian ads | Alt-right Twitter rival may lose domain MORE's chief opponent in the Democratic presidential primary, Sen. Bernie SandersBernard (Bernie) SandersOvernight Defense: Senate passes 0B defense bill | 3,000 US troops heading to Afghanistan | Two more Navy officials fired over ship collisions Senate passes 0B defense bill Dems fear lasting damage from Clinton-Sanders fight MORE (I-Vt.), for his "deep and real" focus on income inequality. 

Biden said Clinton has come up with some "thoughtful" solutions to the issue but that people might question her authenticity on the wage and income gaps because she has only begun speaking about it recently. 

"I think that Bernie is speaking to a yearning that is deep and real. And he has credibility on that," Biden said Monday in an interview with CNN. 

Asked about the fact Hillary has spoken about the issue too, Biden replied, "It's relatively new for Hillary to talk about that."

"Hillary's focus has been on other things up to now," he added. "No one questions Bernie's authenticity on those issues."

Biden said it's not unexpected Clinton would receive scrutiny over her positions but said, "I think she's come forward with some really, really thoughtful approaches to deal with the issue."

Biden's comments could inject even more drama into the Democratic presidential primary race. Polls show Clinton and Sanders running close races in the key early states of Iowa and New Hampshire, defying early predictions of a Clinton landslide victory. 

Clinton, who served as President Obama's secretary of State, is widely perceived to be the favored candidate inside the White House. But for months, Biden weighed jumping into the race to challenge her. He decided this fall not to run while his family and he were still mourning the death of his son, Beau. 

Biden, who has declined to endorse a candidate, met privately with Sanders in October, just after bowing out of the race. 

The vice president said it's not surprising that Sanders is running close with Clinton, explaining that expectations for Clinton were set sky high. 

Despite what early polls in Iowa and New Hampshire showed, "I thought for the last six months they were neck in neck in both places," Biden said.

"I never thought she was a prohibitive favorite," he added. "I don't think she ever thought she was a prohibitive favorite … everything's sort of coming down to Earth."

The vice president also said the issue of gun control wouldn't be a problem for Sanders in the Democratic primary, citing his recent shift on the issue.

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

Obama set a litmus test for Democrats, saying he will not campaign for any candidates who do not back "common sense" gun reforms. The Vermont senator has come under scrutiny from Clinton over his past positions on the issue.  

Biden recently said that while the decision not to run was the right one, he regrets not being in the campaign "every day." But the vice president shut the door to jumping back into race if Clinton falters in Iowa and New Hampshire. 

"No, even if Hillary loses both, it's a long way to go to the nomination," he said. "I don't think there's any door to open."