Richard Painter, a University of Minnesota law professor and prolific TV and Twitter critic of President Donald Trump, said Wednesday that he is forming an exploratory committee that could lead to a campaign for the U.S. Senate seat vacated by Al Franken and now occupied by Democrat Tina Smith.

Painter said at a State Capitol news conference that although he’s a longtime Republican and served as chief ethics lawyer in George W. Bush’s White House, he’s unsure whether he would run as a Republican, Democrat or independent.

“I need to think about whether there’s a place for me” in the GOP, he said. “I’m going to be considering any and all options.” He described himself as “a centrist in many ways — right up the middle.” He said he has supported Democrats.

In response, Matthew Pagano, the Minnesota Republican Party’s executive director, said in a statement: “Clearly Richard Painter isn’t sure what he wants to do and I think that speaks for itself.”

Karin Housley, a small-business owner and suburban state senator, is the only Republican to announce plans to run for the seat. She was elected to the Legislature in 2012.

Painter said that if he runs, he would not accept donations from political action committees, Super PACs or what he called “dark money” groups.

“I have seen corruption firsthand. I have seen corruption in Washington, D.C., and I will emphasize that the corruption we see today is not to be blamed principally on President Donald Trump, even though I have criticized him,” he said. “It is to be blamed on the role of money in politics.” Painter said that issue would drive his campaign.

“This state is entitled to be represented by two senators who are responsible only to the people of Minnesota who elected them, not to special interests,” he said. Painter said he wouldn’t necessarily need a lot of money to mount a campaign. “I’d like to have a lot of support from individual donors,” he said.

Asked if Trump should be impeached, he said congressional committees should consider whether the president has committed abuse of power or obstruction of justice. He declined to say how he would vote in a Senate trial.

Painter recently criticized Housley on Twitter for blaming a long line at the DMV on Smith. Painter later tweeted that Housley had blocked him: “She’s upset that I asked her to talk about serious issues rather than blame 20 minute lines at DMV on her opponent Tina Smith. For example that wait at DMV is 20 minutes more than it takes to register an AR-15.”

Housley’s campaign spokesman Bryan Piligra said in a statement, “It’s important for voters to have a choice in any election, so we welcome our new opponent to the race.”

He added, “Karin Housley has given a voice to the many Minnesotans who are fed up with the dysfunction, partisanship, and obstruction in Washington.”

Painter called Housley and Smith “very good candidates.”

Painter was born in Philadelphia in 1961. He graduated from Harvard and then Yale Law School. He was Bush’s ethics lawyer from 2005-2007.

He is vice chairman of Citizens for Responsibility and Ethics in Washington. That group sued Trump, alleging that he violated the Constitution’s emoluments clause by refusing to sell his assets or put them in a blind trust. The case was dismissed in December.

Painter is the S. Walter Richey professor of corporate law at the University of Minnesota, a job he said he will keep.