The former White House chief ethics lawyer under the George W. Bush administration on Monday announced his bid for a U.S. Senate seat in Minnesota, formerly held by Al Franken (D-MN).

Richard Painter, a longtime Republican, recently filed to run as a Democrat for the seat occupied by Sen. Tina Smith (D-MN), the Star Tribune was first to report. Smith was appointed by the Minnesota governor to serve out the remainder of Franken’s term after he resigned amid allegations of sexual misconduct.

According to the Star Tribune and a tweet from Painter’s Twitter account — Painter For Minnesota — Painter announced his bid at a news conference on Monday morning. Painter already had a campaign website live, Painter For U.S. Senate, before he made the announcement, in which he vowed to not take money from Super PACs.

In a tweet on Monday afternoon, Painter explained why he “QUIT” the Republican party, due in large part to President Donald Trump’s “reckless trade war,” as well as his “attacks on the freedom of the press and of religion, on the judiciary and on his own Justice Department.”

Read Richard's full statement from today on his decision to leave the GOP and seek the Democratic nomation for U.S. Senate. #PeopleForPainter pic.twitter.com/62GEomhEcu — Painter For Minnesota (@RWPMinnesota) April 30, 2018

Painter currently works as a corporate law professor at the University of Minnesota and is a frequent critic of President Donald Trump on cable news and on Twitter. Painter told the Star Tribune last month that he was forming an exploratory committee for a potential run, but was unsure whether he would remain a Republican.

“I need to think about whether there’s a place for me” in the GOP, he said last month, according to the Star Tribune, saying he would be “considering all options.” He also told the Star Tribune that he is a “centrist in many ways.”

Minnesota Gov. Mark Dayton appointed Smith, his former lieutenant governor after Franken resigned, with the hope that she would be the front-running Democrat vying for the seat.

Franken resigned in January after weeks of reports of sexual harassment and multiple women coming forward alleging Franken groped them during photo ops.

Karin Housley, a state senator, is the only Republican who’s announced a bid for open seat.