With a little less than a month left before the Iowa caucuses, Democratic presidential candidates have ramped up their attacks against former Vice President Joe Biden (D).

On Sunday, David Sirota — a speechwriter for Sen. Bernie Sanders‘ (Vt.) campaign — tweeted a video of Biden defending his vote for the Iraq War in 2003, and assailed the former vice president for his support of the war in a series of tweets.

“Nine months ago, I voted with my colleagues to give the President of the United States of America the authority to use force. And I would vote that way again today. It was the right vote then, and it would be the correct vote today.”

Watch his comments below:

https://twitter.com/davidsirota/status/1216379312816787456?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1216379312816787456&ref_url=https%3A%2F%2Fwww.mediaite.com%2Felection-2020%2Fsanders-camp-releases-archival-video-of-joe-biden-praising-bold-leader-george-bush-months-into-iraq-war-i-and-many-others-will-support-him%2F

In a separate statement, Sanders’ senior campaign adviser Jeff Weaver said it is “appalling” that Biden “refuses to admit he was dead wrong on the Iraq War.”

The barrage came after former Secretary of State John Kerry, who has endorsed Biden, said on Friday that Biden was not “in favor” of going to war.

Sanders has used Biden’s support of the Iraq War as a cudgel against Biden before. In an interview with The Washington Post, Sanders said that Biden has “a lot of baggage” and called his record “so weak,” specifically noting Biden’s past support of military intervention in Iraq.

As what was once the most diverse field of presidential candidates winnows, Biden and Sanders appear to be the front-runners for the nomination — leading Vermont senator to savage Biden’s record

Sanders’ increased attacks on Biden come as a new poll found Sanders in first place in Iowa.

Additionally, an average of polls finds that while once-promising candidates for the nomination have dropped out or appear to be losing steam, Biden and Sanders are leading the pack.

As foreign policy has become a larger issue in the primary, Biden appears to have the upper hand over Sanders as two polls found that Democratic voters say they feel Biden could best handle foreign policy issues as president.