House Speaker Nancy Pelosi announced the opening of an official impeachment inquiry into President Donald Trump late Tuesday.

After meeting with the chairs of multiple House of Representatives committees, Pelosi spoke to reporters in Washington.

“The actions taken to date by the president have seriously violated the Constitution, especially when the president says ‘Article II says I can do whatever I want,’” Pelosi said.

The impeachment inquiry centers around Trump allegedly asking the president of Ukraine to investigate former Vice President Joe Biden’s son and threatening to withhold military aid to the country — currently under partial military occupation by Russia — if Ukraine did not do so.

“Today, I’m announcing the House of Representatives is moving forward with an official impeachment inquiry,” Pelosi said.

Mack Shelley, Iowa State professor and chair of the political science department, said before Pelosi’s press appearance, impeachment by the House of Representatives is possible, though at this point Trump’s removal by the Senate is not.

“As long as the Republicans have a relatively good majority in the Senate, which means no more than three members bolt, then nothing is going to happen [on conviction and removal from office],” Shelley said.

It is difficult to find even vulnerable Republican senators who would be inclined to vote to convict and remove the president, Shelley said, a result in part stemming from the Supreme Court ruling on Citizens United v. Federal Election Commission allowing for much greater spending on campaign finance. Should Republican senators step out of line and vote to remove the president, they could expect to be targeted by a primary campaign from the conservative right to unseat them.

Rep. Cindy Axne, D-West Des Moines, said in a statement she took “an oath under God to support and defend the Constitution of the United States.”

“Beyond an abuse of power, allegations that the president threatened to leverage U.S. taxpayer dollars to extort a foreign government, if true, constitute an unequivocal violation of our federal laws and the U.S. Constitution I swore to defend,” Axne said.

Axne’s move on an inquiry is “bold,” Shelley said.

The House of Representatives only needs 218 representatives to vote yes on a single article of impeachment for the president to be sent to a trial in the Senate. The New York Times reports 180 representatives currently support an impeachment inquiry.

“Impeachment is certainly possible, conviction absolutely not under current circumstances,” Shelley said. “Trump famously said during his campaign that he could shoot somebody on Fifth Avenue and not lose votes. That’s not going to happen literally […] but you’re getting fairly close to the moral equivalent of something like that, and does it make a difference to his base — no.”