Biden won't commit to backing Sanders if he's the nominee

Former Vice President Joe Biden has stopped short of saying he'd support Bernie Sanders if the progressive Vermont senator wins the Democratic presidential nomination.

"I'm not going to make judgments now," Biden told reporters in Muscatine, six days before the Iowa caucuses.

"I just think that it depends upon how we treat one another between now and the time we have a nominee." Biden had previously promised to support the Democratic nominee, "regardless" of who it is. At some stops along the campaign trail, Biden has even pledged to "work like hell" to help any of his rivals defeat President Donald Trump.

Yet tensions are rising between Biden and Sanders on the campaign trail. The two men reflect the larger ideological battle between a Democratic establishment in which Biden has spent his career and the progressive left that has surged in influence since Sanders' failed bid for the Democratic presidential nomination in 2016.

The two have jousted over their records on Social Security, foreign policy and trade. Sanders recently apologized to Biden after one of the senator's high-profile supporters penned a column asserting that Biden has a "corruption problem."