As the Hillary Clinton campaign desperately seeks a way to slow Vermont Sen. Bernie Sanders’ political momentum, the head of a pro-Clinton super PAC is expected to begin airing attack ads calling for the 74-year-old Sanders to release his medical records.

According to Politico, David Brock, a former conservative journalist who is now one of Clinton’s most loyal surrogates, will air the ads this weekend through his pro-Clinton super PAC, Correct the Record. The ads will demand Sanders release a clean bill of health before the Iowa caucuses, which will be held next month.

There is no indication that Sanders has health problems. But releasing medical records is a standard practice for serious presidential candidates. Clinton, now 68, released hers in July. Clinton’s doctor determined she was “fit to serve” as president, while noting that she does suffer from “hypothyroidism and seasonal allergies.” She is also on a long-term anticoagulation regimen.

There is no indication that Brock plans to call on former Maryland Gov. Martin O’Malley to release his medical records. The 52-year-old is polling well behind Clinton and Sanders.

It is unclear whether the Clinton campaign was involved in Correct the Record’s plans to call for Sanders’ records. But Brock’s group is allowed to coordinate directly with the Clinton campaign and has mobilized against Sanders before, often doing the messy work that the Clinton team avoids doing itself.

In September, Brock’s group began circulating emails comparing Sanders to Hugo Chavez, the late Venezuelan dictator, and to Jeremy Corbyn, the radical leftist leader of U.K.’s Labour Party.

As campaign finance records show, Clinton’s campaign gave Brock’s group $275,000 last June.

[dcquiz] Clinton’s campaign team and her allies have grown increasingly concerned with the surprising grassroots challenge posed by Sanders. Clinton insiders have said in numerous reports this month that the campaign failed to take Sanders seriously enough. Many are having deja vu of 2008, when then-Illinois Sen. Barack Obama came from behind to defeat Clinton, who was heavily favored to win at the outset of the race.

A senior adviser for Sanders dismissed Correct the Record’s plan.

“These kinds of attacks are going to be employed by a super PAC that directly coordinates with her campaign,” Tad Devine told Politico.

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