By Doina Chiacu and Ginger Gibson
WASHINGTON (Reuters) - U.S. Vice President Joe Biden praised Democratic presidential candidate Bernie Sanders for tapping into Americans' concerns about growing income inequality, potentially giving the Vermont senator a boost as he gains on rival Hillary Clinton weeks before the Iowa caucuses.
Sanders has argued that he is a more authentic choice to be the party's nominee as he tries to undermine Clinton's double-digit lead in national polls by gaining ground in the important early nominating states of Iowa and New Hampshire.
In an interview with CNN on Monday night, Biden said Sanders' focus on the growing gap between the very rich and other Americans has struck a chord with voters.
"Bernie is speaking to a yearning that is deep and real and he has credibility on it," Biden said. "And that is the absolute enormous concentration of wealth in a small group of people with the new class now being able to be shown being left out."
He said Clinton, who is campaigning in Iowa on Tuesday, had not focused on income inequality as long.
"It's relatively new for Hillary to talk about that," Biden said. "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."
On Tuesday, Biden said that was not a criticism of Clinton, a former U.S. secretary of state. He told NBC's "Today" show that her focus had rightly been on foreign policy, while income inequality had long been Sanders' "mantra."
"PUSHING THE ENVELOPE"
"Even when income inequality wasn't as serious as it is today, it was his drumbeat," Biden said. "She's coming up with some very good ideas but Bernie is pushing the envelope on this."
The Biden interviews came before President Barack Obama's final State of the Union address on Tuesday night.
While Clinton has a large national lead in the polls, she has struggled to make solid gains in Iowa and New Hampshire, which hold outsized influence on the election process.
On Tuesday, a Quinnipiac University poll showed Sanders climbed to 49 percent in Iowa, a 5 percentage point lead over Clinton going in to the Feb. 1 caucuses. He widened his lead in New Hampshire by 14 points, a Monmouth University poll said. The polls had an error margin of 4.4 and 4.8 points, respectively.
Biden was courted by some Democrats to seek the presidential nomination but declined, citing family obligations after his son Beau Biden died of cancer last year. Within the party, concerns remain whether Clinton can overcome a lack of enthusiasm among voters.
Biden also told CNN that he and Obama want to influence the presidential nominees in November's White House election, especially on gun control.
Clinton has increasingly criticized Sanders for past votes that were viewed favorably by the National Rifle Association.
Biden said Sanders is making improvements to his position.
"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," Biden said. "People who are schizophrenic and have mental illnesses shouldn't own guns, and he has said that."
For more on the 2016 presidential race, see the Reuters blog, "Tales from the Trail" (http://blogs.reuters.com/talesfromthetrail/)