As he climes to the top of national polls and takes a small lead in Iowa, Bernie Sanders is focusing in on his closest moderate rival, making the argument that Joe Biden’s electability case isn’t all it’s cracked up to be. In recent days, Sanders has launched a multi-front attack on Biden, blasting his experience as Washington baggage and asserting that the former VP lacks the juice to truly inspire Democratic voters.

Citing unsavory aspects of Biden’s record, including his previous support for the Iraq war, Sanders told Anderson Cooper Monday that Biden couldn’t inspire the “huge voter turnout” it would take to defeat Donald Trump. “I just don’t think that that kind of record is going to bring forth energy that we need to defeat Trump,” Sanders said—remarks that echoed comments he made in Iowa to the Washington Post last week. “It’s just a lot of baggage that Joe takes into a campaign, which isn’t going to create energy and excitement,” Sanders said at the time. “He brings into this campaign a record which is so weak that it just cannot create...excitement and energy.”

Biden, the once and future frontrunner, has had a target on his back since he entered the race. Elizabeth Warren has also criticized him from the left, and more recently, Pete Buttigieg has challenged him for the center lane. But Sanders’ broadsides could be the most potent, contrasting the enthusiasm Sanders has drawn on the campaign trail—as evidenced by the massive amounts of money he’s raised from grassroots donors—with Biden’s own struggle to inspire fundraisers. Recent polling backs him up. While Iowa likely Democratic voters support Sanders and Biden in equal measure, almost 70% of Sanders supporters were “enthusiastic” about their vote choice, compared to 49% of Biden supporters.

That could give Sanders a real foothold. As the Post reported, his campaign increasingly views taking on Biden as strategically important in anticipation of a protracted two-person race to the nomination. “Joe Biden and the Bernie Sanders campaign are talking to a lot of the same people,” Sanders adviser Pete D’Alessandro told the Post. While some Democrats worry that Sanders is too far left to win a general election, Sanders is looking to play up Biden as an avatar for the very establishment that failed to beat Trump in 2016. “The way you defeat Donald Trump is by having the largest voter turnout in the modern history of this country,” he told the Post. “That’s how you beat him.”

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