The House has just finished an impeachment inquiry of President Trump over allegations that he pressured Ukraine to investigate his political rivals. Now they could vote on whether to impeach him by Christmas. Here is what you need to know about the impeachment process and the politics of this inquiry.

What is impeachment?

It is a constitutional mechanism that allows Congress to determine that the president is no longer fit to serve and should be removed from office. Article II of the Constitution sets up the presidency and executive branch but also lays out a way to remove the president. The key clause is: “The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.”

The clause is generally understood to mean a violation of the oath of office, not a crime in the traditional sense of breaking the law. That means there doesn’t have to be clear evidence of a crime for Congress to impeach the president.

Who can impeach the president?

Congress. Specifically, the House. It’s up to the House to decide what meets an impeachable offense.

But impeaching the president is not the same thing as removing the president from office. To determine whether that happens, the Senate must hold a trial presided over by the chief justice of the United States. We’ll get to how that works.

Which presidents have been impeached?

Two U.S. presidents have been impeached: Andrew Johnson and Bill Clinton. Richard M. Nixon resigned under the threat of impeachment. None were removed from office via a Senate trial. The vice president would become president after a successful impeachment.

So, wait, is impeachment happening?

Yes, but this is a new development. House Speaker Nancy Pelosi (D-Calif.) embraced an impeachment inquiry in September, authorizing lawmakers on three key committees to look into whether there was enough evidence to impeach Trump. They spent two months interviewing national security officials and diplomats in the Trump administration to determine whether Trump inappropriately politicized diplomacy with Ukraine. Those impeachment investigators released a 300-page report the first week of December alleging that Trump leveraged the State Department and taxpayer money to try to get Ukraine to announce investigations of his political rivals.

Now it’s the House Judiciary Committee’s job to take that report and write up articles of impeachment against Trump. It is expected to have articles for the full House to vote on by Christmas.

Why did Democrats decide to start an impeachment inquiry of Trump?

Then the White House released a rough transcript of the July 25 call with Ukrainian President Volodymyr Zelensky. It shows that Trump asked the Ukrainian president for “a favor, though”: to investigate the Bidens and a conspiracy theory that Ukraine interfered in the 2016 presidential election, not Russia. To a number of Democrats, that call alone was a potentially impeachable offense because Trump was soliciting election help from a foreign power. More than a dozen Republican lawmakers have said the call wasn’t okay.

Then, Trump’s acting chief of staff, Mick Mulvaney, said that the White House held up bipartisan military aid to Ukraine to try to get Ukraine’s president to agree to investigate the 2016 election, potentially befitting Trump politically.

What is happening with Trump’s impeachment?

The House spent October bringing in 17 witnesses to testify behind closed doors. Then they asked a dozen to testify publicly in November.

Much of the testimony substantiated the allegations that Trump allies pressured Ukrainian officials to open investigations that would be politically beneficial to Trump to get their White House meeting and military aid.

Gordon Sondland, the U.S. ambassador to the European Union, was the diplomat who appeared to be doing much of Trump’s bidding in Ukraine, and he said he relayed a quid pro quo request to a Ukrainian official that amounted to: They’ll get their military aid when they announce an investigation of the Bidens and 2016.

“I know that members of this committee have frequently framed these complicated issues in the form of a simple question: 'Was there a ‘quid pro quo?’ ” Sondland testified. “As I testified previously, with regard to the requested White House call and White House meeting, the answer is yes.”

Lt. Col. Alexander Vindman is a Ukraine expert on the National Security Council who listened to Trump’s July call with Ukraine’s president and was so alarmed by the pressure he heard Trump put on Zelensky that he notified a National Security Council lawyer about his concerns. That lawyer, John Eisenberg, then proposed moving the call transcript to a secret server with restricted access — an unusual step.

Vindman and Fiona Hill, another top national security aide, both testified that the quid pro quo was linked to Trump’s acting chief of staff, Mulvaney.

Other State Department and White House officials testified that Trump’s personal lawyer Rudolph W. Giuliani was conducting a shadow foreign policy in Ukraine, pushing false narratives fed to him by Ukrainians with an ax to grind with Marie Yovanovitch, the U.S. ambassador to Ukraine. She testified that Trump had her ousted over concerns that she had been critical of him and was loyal to the Bidens. She also questioned whether her focus on anti-corruption could have jeopardized some of Giuliani’s clients in Ukraine.

After a November blitz of public hearings, the Judiciary Committee held a hearing the first week of December featuring constitutional experts picked by Democrats who explained why they thought Trump’s actions merited impeachment. (One expert picked by Republicans argued that it was too soon to move forward based on the evidence at hand.) They’re expected to hold hearings the second week of December on what the articles of impeachment should be.

Will the Senate remove Trump from office if the House impeaches him?

There is no indication that it will. At least 15 Senate Republicans have expressed reservations or concerns about Trump’s actions as they relate to asking foreign governments for political help, but none have said they would vote to impeach him. Most Senate Republicans support Trump. So right now the math is in the president’s favor. To remove him from office, it would take at least 20 Republican senators to join Senate Democrats and vote to remove him. As new revelations come out, Senate Republicans are lying low, trying not to comment on what’s happening.

Senate Majority Leader Mitch McConnell (R-Ky.) said a trial would probably mean the Senate meets six days a week. There are talks of having it drawn out for more than a month into the Iowa caucuses in February, or rushing it through in as little as two weeks. The White House wants to make the trial a big, televised drama, featuring lots of witnesses, believing that it’s the best way to defend Trump.

Could Trump run in 2020 even if he’s impeached?

If he is impeached by the House, yes. If he is removed from office, well, that has never happened before, so we would probably all be armchair-interpreting the Constitution to figure that one out. In the past two impeachment trials, the Senate has taken two votes, said Josh Chafetz, a law professor at Cornell: one to convict or acquit the president and thus remove him from office; and the other on whether to bar him from running again.

Could impeachment go into 2020?

It almost certainly will. In the House, Pelosi wants to act while there’s momentum and hold a vote by the end of the year. Politically, it could be much more difficult to make their case that impeachment is necessary if it’s 2020 and nearing an election in which Trump could be voted out of office anyway. But once the House votes on whether to impeach him, the process is only halfway done.

What do the polls say about an impeachment inquiry?

Americans have been skeptical of an impeachment inquiry. But that changed as more evidence supporting a whistleblower’s complaint was released. A Washington Post-Schar School poll out the first week of October found that a majority of Americans, 58 percent, say that the House was right to open an inquiry. And 49 percent think Trump should impeached and removed from office. That’s before the inquiry is even over. Still, Americans are split overall on impeachment: A November Washington Post-ABC News poll finds that 47 percent say Trump should not be impeached.

What is Trump saying about the impeachment inquiry?

The morning after public hearings in the inquiry wrapped up, Trump went on Fox News Channel and accused a witness who overheard him ask about “investigations” of lying, repeated a debunked theory that Ukraine interfered in the 2016 election and threatened to reveal the whistleblower’s identity.

He has deployed a bevy of other falsehoods to defend himself as evidence mounts that he tried to politicize diplomacy for his benefit. And Republicans in Congress are echoing them, throwing out more than 26 defenses throughout the private and public impeachment inquiry hearings.

What resources do you have so I can follow the impeachment inquiry?

Glad you asked. Beyond breaking news on washingtonpost.com, we have:

The 5-Minute Fix impeachment newsletter, in your inbox every weekday afternoon.

What happened in impeachment this week? will be posted every Friday afternoon on The Fix