Julián Castro, the secretary of Housing and Urban Development and rumored Democratic vice presidential prospect, violated a law prohibiting federal employees from politicking on the job when he commented on the presidential election in an April interview with Katie Couric, the U.S. Office of Special Counsel said Monday.

Castro, the former mayor of San Antonio, praised Hillary Clinton as the “most experienced, thoughtful and prepared candidate for president that we have this year” and described Donald Trump as unfit for the office in an interview with Couric for Yahoo News on April 4.

The special counsel found that those remarks violated the federal Hatch Act because Castro had given the interview in his “official capacity” as HUD secretary, OSC’s Carolyn N. Lerner wrote to President Barack Obama in a letter referring the counsel’s findings “for appropriate action.”

The report, dated June 24, notes that Castro told Couric he was “taking off my HUD hat” before he made his comments on Clinton and Trump. Still, the OSC concluded that his “statements during the interview impermissibly mixed his personal political views with official agency business,” according to Lerner’s letter.

According to the report, Castro testified that he believed at the time of the interview that his comments were in line with the law and never intended to violate it. He has since “reconsidered this position” on the appropriateness of the remarks and said he is “confident no similar blurring of roles will occur in the future,” the report says.

“I now have watched the recording of the interview and appreciate that, while my intention was to avoid any blurring of roles and make clear that I was not speaking as a representative of HUD, that fact may not have been obvious to viewers,” Castro said, according to the report.

Castro is viewed as a possible running mate for Clinton in the November election. Lerner’s letter to Obama referenced the election and suggested that the OSC’s report on Castro “offers an opportunity to deter violations by reminding federal employees of the Hatch Act’s restrictions.”