Impeachment talk was kept mostly to a whisper during President Donald Trump’s first two years in office. It may grow louder as opposition Democrats take control of the U.S. House of Representatives, where the formal charges known as articles of impeachment originate. But Democratic leaders haven’t been ready to suggest that Trump committed the “high crimes and misdemeanors” that would warrant an attempt to remove him from office.

1. Will House Democrats propose impeaching Trump?

A handful have already done so, offering resolutions alleging that Trump committed offenses warranting removal from office. Those include obstructing justice, accepting what’s known as emoluments, sowing racial discord and undermining the federal judiciary. But introducing such resolutions is easy; getting a majority to support them is the challenge. (When one reached the House floor, it was defeated 355 to 66.) Until now, party leaders have mostly steered way from impeachment talk, reasoning that many voters aren’t eager to see a repeat of the warfare that raged 20 years ago when Republicans sought to remove President Bill Clinton. The pro-impeach movement has been largely driven by activists outside Congress, like billionaire Tom Steyer.

2. What could turn the tide?

Special Counsel Robert Mueller, who is overseeing the criminal investigation into Russian interference in the 2016 campaign, could choose to submit a written report to Congress alleging misdeeds by Trump. Or Democrats could uncover alleged wrongdoing in the investigations they’re expected to open when they take control of the House in January. There’s also the fact that Trump has been implicated — though not charged — in a criminal act: the payment of hush money to two women before the 2016 election. Trump’s former personal lawyer, Michael Cohen, made that allegation while pleading guilty on Aug. 21 to tax evasion, making false statements to a bank and making illegal campaign contributions.

3. What are impeachable offenses?

Congress decides. The U.S. Constitution says the president — along with the vice president and “all civil officers,” which has been construed to include judges and members of a president’s cabinet — “shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes and misdemeanors.” As Congress has defined it through the years, the phrase “high crimes and misdemeanors” includes exceeding or abusing the powers of the presidency, or misusing the office for improper purpose or gain.

4. What about offenses committed before becoming president?

They might normally be considered outside the purview of impeachment. But what Trump is accused of — arranging to pay women to keep unflattering information from the public while campaigning for the presidency — may be “precisely the sort of offense that the drafters of the Constitution meant to cover in granting Congress the power to impeach and remove a president,” Adam Liptak wrote in the New York Times.

5. How exactly does impeachment work?

House lawmakers can introduce impeachment resolutions like ordinary legislation, or the entire House can vote to authorize an inquiry into whether impeachment is warranted. Either way, the matter then would normally go to the House Judiciary Committee, which can choose to hold hearings and/or vote to send one or more articles of impeachment — formal written charges — to the full House. Any article approved by a majority of the House goes to the Senate.

6. What happens in the Senate?

In one of the more unusual spectacles in American politics, the 100 members of the Senate become the jury in a trial, with some members of the House functioning as prosecutors and the chief justice of the Supreme Court presiding (if the accused is the president). Witnesses are called, and evidence submitted, with House impeachment managers and counsel for the accused giving opening and closing statements. If two-thirds of the Senate, or 67 senators, vote to convict, the official is ordered removed from office.

7. How often has this happened?

The House has initiated impeachment proceedings more than 60 times, according to its historian’s office, and voted to impeach 15 federal judges, one senator, one cabinet secretary and two presidents — Andrew Johnson in 1868 and Bill Clinton in 1998. Eight judges were convicted and removed from office.

8. How many presidents have been removed by impeachment?

Technically speaking, none. Johnson, impeached by the House for firing the secretary of war, survived because the Senate fell just one vote short of a two-thirds majority to remove him. Fifty senators voted to remove Clinton for obstruction of justice, and 45 voted to remove him for perjury, also shy of the two-thirds majority. Richard Nixon resigned the presidency in 1974 when it became clear he would be impeached by the House and convicted by the Senate. The House Judiciary Committee had approved three articles of impeachment accusing him of obstruction of justice, abuse of power and contempt of Congress, for his role in covering up the politically motivated break-in of Democratic National Committee headquarters at Washington’s Watergate office building.

9. What would happen if Trump were removed from office?

Vice President Mike Pence would automatically be elevated to the presidency. He would then appoint a vice president, subject to a majority vote in both houses of Congress. In this very hypothetical scenario, a President Pence could himself run twice for re-election, in 2020 and 2024, were he to succeed Trump after Jan. 20, 2019, halfway through Trump’s term. Oh, and there’s this: Unless the Senate voted separately to disqualify Trump from public office, he could, legally, run again.