The Senate is postponing the confirmation hearing for White House physician Dr. Ronny Jackson, Trump’s pick to lead the Department of Veterans Affairs.

Democrats and Republicans alike had raised concerns about Jackson’s qualifications to oversee the second-largest federal agency, given his lack of management experience. But it now appears other issues have arisen in connection to his management of the White House medical office, according to the Washington Post.

What those issues are remain a mystery — but they’ve apparently generated enough bipartisan concern to prompt a last-minute delay of the hearing, which had been scheduled for Wednesday.

CNN reported Monday that Democratic and Republican senators are reviewing allegations “related to improper conduct in various stages of his career.” Axios previously reported that questions about Jackson’s “professional conduct” were brought to attention of Sen. Jon Tester (D-MT), the ranking member of the Senate Veterans Affairs Committee. The Washington Post cited “concerns about his qualifications and oversight of the White House medical staff.”

“We’re going to vet him. The Trump administration doesn’t do a particularly good job,” Sen. Sherrod Brown (D-OH) told Politico. “That’s all I’m going to say.”

The vagueness surrounding these allegations complicates Jackson’s path toward confirmation as VA secretary. Trump selected Jackson, his personal physician, after ousting David Shulkin in March. It was a surprising choice, even for Trump, and seemed to be based more on the president’s warm feelings toward his doctor than Jackson’s management and policy qualifications to lead the sprawling federal agency.

Jackson, in fact, is probably best known for his effusive evaluation of Trump’s mental and physical health, which he delivered in a lengthy press conference after the president’s physical back in January. “It is called genetics. ... Some people have just great genes,” Jackson said during the briefing. “I told the president that if he had a healthier diet over the last 20 years, he might live to be 200 years old.”