Clinton’s vote became a major vulnerability when she ran against then-Sen. Barack Obama (D-Ill.) for the Democratic presidential nomination in 2008. Biden’s backing for the war remains a sore point for some on the left even now.

“The elites and the establishment are going to try to say that because Joe Biden sat next to Barack Obama he has the most ‘foreign policy credentials,’ but that is insane,” said progressive strategist Jonathan Tasini, who supports Sanders. “Joe Biden made one of the worst foreign policy blunders ever by voting for the Iraq War, which shows he is completely without judgment.”