Pro-Clinton super PAC Correct the Record will begin airing attack ads, calling for Senator Sanders to release his medical records.

The new assault on Senator Sanders comes as the polls tighten in Iowa, and he holds a commanding lead in the first primary state of New Hampshire.

The ad will reportedly call for Sanders to release his medical records before Iowans go to caucus on February 1st.

“With just two weeks to go before the Iowa caucuses, the super PAC coordinating with Hillary Clinton’s campaign is reportedly launching one of the most desperate and vile attacks imaginable: they are insinuating Bernie is too old and unhealthy to be our next president,” Sanders’ campaign manager Jeff Weaver said in an email to campaign supporters.

“Bernie is in excellent health. But this personal attack is another example of a sickness in our democracy when it is so easy for millionaires and billionaires to buy up candidates and elections.”