Third Way, a center-left think tank, will send roughly 300 prominent Iowa Democrats a memo on Tuesday warning that supporting Vermont Sen. Bernie Sanders in the Democratic primary is what “Trump wants you to do.”

The memo, which was obtained by TIME and first reported by Iowa Starting Line, comes less than a week before the first-in-the-nation caucuses in Iowa on Feb. 3, just as Sanders appears to be solidifying his support in early states. Multiple polls now indicate that Sanders is among the top two candidates, either narrowly leading or narrowly trailing former Vice President Joe Biden.

“Before you vote, we urge you to consider at least a few of the many things in Bernie Sanders’ long record in public life that make him the Trump team’s ‘ideal Democratic opponent,'” the memo reads. It then offers a list of attacks that the Trump campaign could use against the Vermont senator, who identifies as a democratic socialist: “They will call him a socialist…They will say that he thinks the middle class wants to pay more in taxes…They will say he’s backed anti-American radicals.”

“Committed Democrats, like us, would vote for Sanders against Trump,” the memo warns. “But no Democrat remotely as far left as Sanders has ever won the presidency, and swing voters in crucial states would reject the radicalism of Sander’s background and ideas.”

Third Way has long been critical of Sanders, but the timing of the memo is indicative of a renewed concern as Sanders’ prospects rise in the days before the primary officially begins. Third Way is not alone: others in the Democratic establishment have also begun ringing alarm bells about Sanders’ ability to win against Trump.

The Sanders campaign, which TIME reached for comment, largely dismissed the Third Way memo, arguing that Republicans could label any of the Democratic candidates “socialist.”

“All Democrats, even Wall Street-funded groups like Third Way, should be ecstatic to witness [Sanders’] movement attracting new supporters to strengthen the party and expand the electorate,” Sanders campaign manager Faiz Shakir said in a statement. “To win seats up and down the ballot, we need to generate excitement and enthusiasm that drives a huge voter turnout among working people, not stifle it to protect special interests. Bernie Sanders has demonstrated over the course of this primary that this campaign is able to do that—and that’s why Donald Trump is nervous.”

The Sanders campaign also pointed to recently reported audio in which Trump said it would have been “tougher” to win had Hillary Clinton chosen Sanders as her running mate.

The Third Way memo criticizes Sanders for calling for tax increases on the middle class and warn that vulnerable Democratic lawmakers would be forced to break with Sanders, splitting Democrats as they battle challengers in key districts. The think tank also cites some of Sanders’ decades-old writings, which the memo warns will be described as “truly offensive and crazy.” (Sanders grappled with much of that criticism in his first presidential run.)

The memo also argues that some of Sanders‘ proposals are so ambitious that he does not know how much they will cost or how they will be paid for, citing a Sanders quote from a recent CBS News interview. The memo pushes Democrats to use the hashtag “#GoogleBernie,” urging potential supporters to dig into the Senator’s record. Sanders’ supporters often cite his long record as a reason for backing him.

“Right now, in a very crowded field, Sanders is able to get enough support that he could potentially win Iowa. And that would be very bad for the Democratic party and its chances of beating Trump,” Jonathan Cowan, the president of Third Way, told TIME in an interview. A lot of what is in the memo, Cowan argues, is unknown to most voters.

The memo does not mention a recent incident in which Sanders tweeted a supportive comment from problematic podcast host Joe Rogen, and quickly came under criticism from groups including the Human Rights Campaign and progressive group MoveOn.

It’s unclear whether Third Way’s memo will impact the outcome of the Iowa caucus. The Sanders campaign’s base of support is drawn largely from a grassroots movement, unlikely to be fazed by admonitions from a Washington-based think tank.

“No doubt, Sanders and his supporters will impugn our motives rather than respond to the facts in this memo,” the memo says. “But it’s not about us; it’s about him. If Bernie Sanders becomes the nominee, Trump’s odds of winning a second term go up dramatically.”

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Write to Lissandra Villa at lissandra.villa@time.com.