“I’m endorsing him because I know him, I’ve seen him at work, I watched him handle many different situations.”

Bradley, 76, said he would travel to New Hampshire in upcoming weeks to stump for Biden. The former New Jersey senator came within 4 percentage points of beating Gore in the state's 2000 primary. Bradley, who served with Biden in the Senate and has known him for four decades, will also hold events in other early states and help raise money for the campaign.

Bradley’s backing is the latest in a long line of endorsements for Biden, who leads in national polls but is locked in a tight race with three other Democrats in Iowa ahead of its Feb. 3 caucuses. In 2008, Bradley backed Barack Obama after the Iowa caucuses and just before New Hampshire.

In Iowa, Biden has garnered support from big political names who carry sway locally, including swing-district congresswoman Abby Finkenauer and former governor and Secretary of Agriculture Tom Vilsack and his wife, Christie. Those endorsements, however, lack the star power offered to Bernie Sanders by the likes of Alexandria Ocasio-Cortez, who helped draw crowds of thousands for the Vermont senator in the run-up to the caucuses.

Bradley brushed aside the contention among the left flank of the party that Biden is out of step with today's progressives. Despite his consistent national lead, Biden has failed to electrify crowds.

“I think Joe Biden will be the most progressive president we’ve had since Lyndon Johnson — as well as being the most experienced president since Lyndon Johnson,” Bradley said. “I think he understands that you’ve got to get things passed, you’ve got to get a Congress that’s Democrat — House and Senate. You’ve got to have those things to make progressivism a reality."