Bernie Sanders's campaign ratcheted up its attacks on Joe Biden's claim that he did not support the Iraq War nearly as soon as it started.

“It is appalling that after 18 years Joe Biden still refuses to admit he was dead wrong on the Iraq War, the worst foreign policy blunder in modern American history," Sanders senior adviser Jeff Weaver said in a statement Saturday. "Unlike 23 of his Senate colleagues who got it right, Biden made explicitly clear that he was voting for war, and even after the war started, he boasted that he didn’t regret it."

Biden voted for the Iraq War in 2002 while he was a Delaware senator, but he has claimed several times on the campaign trail that he opposed the effort “from the moment” the March 2003 invasion started. The then-senator expressed support for the war, saying in July 2003 that he still thought the job was “doable.” In a Senate floor speech, Biden said, “I voted to go into Iraq, and I'd vote to do it again."

He later changed his position. As vice president, Biden oversaw the withdrawal of nearly 150,000 troops from Iraq in 2011, which many argue fueled the rise of the Islamic State.

"Bernie Sanders saw the same information and had the judgment to vote against the Iraq War," Weaver said. "That’s the kind of commander in chief we need — someone with the toughness and judgment to get those calls right, not someone who undermined Democratic opposition, enthusiastically supported a disastrous war, refuses to admit mistakes, and then tries to rewrite history.”

Foreign policy shot to prominence in the Democratic presidential field after President Trump ordered a strike that killed of Iranian Revolutionary Guard Quds Force leader Gen. Qassem Soleimani on Jan. 2, changing the landscape of Middle East policy. Sanders argued that the move puts the United States on the path to another war.

Despite flaunting in Iowa last week that his supporters "have not heard me disparage any of the candidates," Sanders has been increasing his attacks on the former vice president as the the Feb. 3 first-in-the-nation Iowa caucuses loom.

“You know, Joe Biden has been on the floor of the Senate, talking about the need to cut Social Security or Medicare or Medicaid,” Sanders said in an interview on Monday. “Joe Biden pushed a bankruptcy bill, which has caused enormous financial problems for working families. So, if we're going to beat Trump, we need turnout. And to get turnout, you need energy and excitement.”

With Sanders being the top second choice among likely Democratic primary voters who say they support Biden, part of his strategy to securing the Democratic presidential nomination includes winning over a portion of those Biden supporters.

The most recent poll of likely Democratic caucusgoers in Iowa shows Sanders leading the field with 20% support and Biden in fourth place with 15% support.