President Trump has been impeached by the House of Representatives, and on Wednesday, the Senate will vote on whether to convict him and remove him from office.

The outcome of that vote is pretty certain: Enough senators have already said they will vote against removing him to assure his acquittal.

[The latest reporting and analysis on impeachment proceedings against President Trump]

Here’s what you need to know about how the process of impeaching President Trump has worked, and how we got here.

How the Senate trial works

The Constitution requires senators to serve as jurors who decide whether to convict the president and remove him from office on charges made by the House through articles of impeachment: in this case, abuse of power and obstruction of Congress.

Each day of the trial, they enter the Senate chamber, surrender their phones and take their seats.

After a contentious debate on the parameters for the trial, each side spent three days explaining their case, a process that finished a week after the trial got started.

After the arguments, senators got two days to ask questions of both sides — but only in writing. Chief Justice John G. Roberts Jr., who is presiding over the trial, read them out loud, and Trump’s lawyers or House prosecutors answered them.

[The most interesting questions in the Senate Q&A]

The Senate voted on Friday, Jan. 31 not to continue the trial and let both sides subpoena witnesses. That set up the final vote vote.

Senate trial 67 votes needed to convict 53 Republicans 45 Democrats 2 Independents who caucus with Democrats 2/3 of Senate votes to convict Trump is removed. 2/3 threshold not met Trump remains in office. Senate trial 67 votes needed to convict 53 Republicans 45 Democrats 2 Independents who caucus with Democrats 2/3 of Senate votes to convict. 2/3 threshold not met Trump is removed. Trump remains in office. Senate trial 67 votes needed to convict— 53 Republicans 45 Democrats 2 Independents who caucus with Democrats 2/3 of Senate votes to convict 2/3 threshold not met Trump is removed. Trump remains in office. Senate trial 67 votes needed to convict— 53 Republicans 45 Democrats 2 Independents who caucus with Democrats 2/3 of Senate votes to convict 2/3 threshold not met Trump is removed. Trump remains in office.

The battle over witnesses

Four Republican senators needed to cross party lines and vote with Democrats to keep the trial going and call new witnesses. That didn’t happen.

Trump’s acquittal was highly likely all along, so this vote was the one to watch. It would have meant the Senate would be introducing new evidence that House Democrats couldn’t get access to because Trump prohibited his current and former aides from cooperating with House impeachment investigators. But if the Senate approves witnesses, Trump’s defense could also call their own, and some Senate Republicans have pushed the idea of voting for witnesses to force Hunter Biden and the whistleblower to testify.

Democrats said they want to call four current and former White House aides who could help them piece together whether Trump specifically held up Ukraine’s military assistance to extract political favors from Ukraine.

Mick Mulvaney

He is Trump’s acting chief of staff. Other witnesses have said Mulvaney knew about the leverage Trump wanted to use to apply pressure to Ukraine; Mulvaney even said as much publicly. “[Did Trump] also mention to me, in the past, that the corruption related to the DNC server? Absolutely, no question about that. But that’s it. And that’s why we held up the money.” He later said there was no quid pro quo for the Ukraine aid. But the New York Times reported he was involved in trying to get the aid frozen starting in June.

John Bolton

He was serving as Trump’s national security adviser as the Ukraine negotiations were going on during the summer. And Bolton claims he heard Trump say the very thing Democrats allege: that Trump said he would release the military aid for Ukraine only if they announced investigations into former vice president Joe Biden. That’s according to a manuscript of Bolton’s upcoming book, reported on by the New York Times.

Robert Blair

He’s the top adviser to Mulvaney. When Mulvaney asked if it was possible to hold up the aid, it was Blair he was talking to. Blair seemed to carry out much of the action. “We need to hold it up,” he told budget officials at one point, the New York Times reported. Blair, like Mulvaney, may also know more about why Trump wanted the aid held in the first place. The Times reported he was in meetings with Trump when the president expressed skepticism of Ukraine.

Michael Duffey

He’s a top White House budget official. A new email shows he told the Defense Department that Trump wanted it to stop the process of giving the money to Ukraine — and to keep it quiet. This happened less than two hours after Trump’s July call with Ukraine’s president in which Trump asked for political favors. “Clear direction from POTUS to continue to hold,” Duffey wrote in an email obtained by the Just Security blog over the holidays. When the aid freeze was out in the open, other obtained emails show he pinned the blame for the aid freeze on the Defense Department. “You can’t be serious. I’m speechless,” was the Pentagon’s reply.

Here’s how long we think the trial could last

Senate rules say the trial needs to happen six days a week until a vote to convict or acquit the president. It starts at 1 p.m. each day and goes through the evening. Even the shortest possible trial, two or three weeks, is expected to overlap with the 2020 presidential campaign and potentially Trump’s State of the Union address. President Bill Clinton’s trial lasted five weeks, forcing him to give a State of the Union address while it was still going on.

Elections Key dates in Senate trial Possible trial days State of the Union January 2020 S M T W T F S 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 15th Impeachment articles sent to Senate. 16th Senators sworn in. 21st Rules for trial are set. 22nd Opening arguments begin. February 2020 S M T W T F S 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 3rd The Iowa caucuses. 4th The State of the Union. 7th Democratic primary debate in N.H. 11th New Hampshire primaries. 19th Democratic primary debate in Las Vegas. 22nd Nev. Democratic presidential caucuses. 25th Democratic primary debate in S.C. 29th S.C. Democratic presidential primary. DANIELA SANTAMARIÑA/THE WASHINGTON POST Elections State of the Union Key dates in Senate trial Possible trial days January 2020 Jan. 2020 S M T W T F S 15th Impeachment articles sent to Senate. 01 02 03 04 16th Senators sworn in. 05 06 07 08 09 10 11 21st Rules for trial are set. 12 13 14 15 16 17 18 22nd Opening arguments begin. 19 20 21 22 23 24 25 26 27 28 29 30 31 Feb. 2020 February 2020 3rd S M T W T F S The Iowa caucuses. 01 4th The State of the Union. 02 03 04 05 06 07 08 7th Democratic primary debate in N.H. 09 10 11 12 13 14 15 11th New Hampshire primaries. 16 17 18 19 20 21 22 23 24 25 26 27 28 29 19th Democratic primary debate in Las Vegas. 22nd Nev. Democratic presidential caucuses. 25th Democratic primary debate in S.C. 29th S.C. Democratic presidential primary. DANIELA SANTAMARIÑA/THE WASHINGTON POST Elections State of the Union Key dates in Senate trial Possible trial days January 2020 February 2020 S M T W T F S S M T W T F S 01 02 03 04 01 05 06 07 08 09 10 11 02 03 04 05 06 07 08 12 13 14 15 16 17 18 09 10 11 12 13 14 15 19 20 21 22 23 24 25 16 17 18 19 20 21 22 26 27 28 29 30 31 23 24 25 26 27 28 29 15th 3rd Impeachment articles sent to Senate. The Iowa caucuses. 16th Senators sworn in. 4th The State of the Union. 7th Democratic primary debate in N.H. 21st Rules for trial are set. 22nd Opening arguments begin. 11th New Hampshire primaries. 19th Democratic primary debate in Las Vegas. 22nd Nev. Democratic presidential caucuses. 25th Democratic primary debate in S.C. 29th S.C. Democratic presidential primary. DANIELA SANTAMARIÑA/THE WASHINGTON POST

Chief Justice Roberts’s role in overseeing a trial

Roberts’s role is more procedural than that of a judge in a criminal trial. His job is to enforce the rules the senators set for the trial, and to enforce decorum. On one of the first days, Roberts admonished both sides for fighting, saying that House managers and White House lawyers should “remember that they are addressing the world’s greatest deliberative body.”

Roberts doesn’t want to inject himself into politics, says Supreme Court watcher Russell Wheeler with the Brookings Institution. He and Trump also have had a strained history at points, with Roberts at one point offering a rebuke of Trump about the independence of the judiciary.

Here are the Democrats prosecuting the case against Trump

They’re called impeachment managers.

House Intelligence Committee Chairman Adam B. Schiff (D-Calif.): House Speaker Nancy Pelosi (D-Calif.) made him the face of the impeachment inquiry in part because he had already been dueling with the Trump White House over the Russia investigation and has a knack for distilling information in a way that needles Trump’s soft spots, like his Russia connections. Now he’s the lead manager.

House Judiciary Committee Chairman Jerrold Nadler (D-N.Y.): He brought impeachment down the home stretch, helping draft the two articles and guiding their passage on the House floor. He also has three decades of experience in Congress.

Rep. Zoe Lofgren (D-Calif.): She is one of the most experienced members of Congress on impeachment. She was a Judiciary Committee staffer during President Richard M. Nixon’s impeachment proceedings and a member of the Judiciary Committee during the Clinton impeachment.

Rep. Hakeem Jeffries (D-N.Y.): He is No. 5 in the House leadership and a member of the House Judiciary Committee. He’s a lawyer by trade and has experience with the other side of the courtroom from when he clerked for a federal judge in New York. “A seriously respected litigator,” Pelosi said of him.

Rep. Val Demings (D-Fla.): She is a member of two committees involved in impeachment, the intelligence and judiciary committees, which means she is very familiar with the evidence Democrats gathered against Trump. She also was the first female police chief in Orlando, and Pelosi cited her law enforcement background as a strength in a Senate trial. “She knows her way around the courtroom,” she said.

Rep. Jason Crow (D-Colo.): The first-term congressman is one of the most unusual picks because he didn’t sit on any of the impeachment committees. He served as an Army Ranger, leading combat units in Iraq and Afghanistan, and was a partner at a law firm. He does represent the kind of suburban district that Democrats will need to hold onto to keep their majority this year. “He, too, is a respected litigator,” Pelosi said.

Rep. Sylvia Garcia (D-Tex.): She’s also in her first term and before coming to Congress was a long-standing municipal judge in Houston, breaking through many glass ceilings as a Latina on her way to Congress. She also sat on the House Judiciary Committee and would defend Democrats’ inquiry on Fox News.

Here are more details about why Pelosi picked such a politically diverse group.

The clerk of the House of Representatives, Cheryl L. Johnson, and the sergeant at arms, Paul D. Irving, lead a procession with the articles of impeachment through National Statuary Hall on the way to the Senate on Jan. 15. (Matt McClain/The Washington Post)

Here are the top lawyers on Trump’s defense team

Pat Cipollone, White House counsel: He’s a corporate lawyer who some in the administration worry might not have the flair for the dramatic that Trump craves from his defenders. But he also has a trusted relationship with the president and wrote a fiery letter to House Democrats signaling the White House’s refusal to participate in the impeachment inquiry.

Jay Sekulow, Trump personal lawyer: He represented Trump against Robert S. Mueller III during the special counsel’s investigation and could argue in the Supreme Court for why Trump’s financial records should be kept from investigators. He is familiar with the spotlight as host of his own weekly radio show and a frequent television commentator.

Alan Dershowitz, Harvard law professor: He has said he voted for Hillary Clinton in 2016 and expressed support for Biden in 2020. But since Trump got elected, he has been one of the most prominent legal voices defending the president, especially from the special counsel investigation into Russian election interference and obstruction of justice. He has met with the president several times, and in 2018, before the Ukraine allegations, he published a book, “The Case Against Impeaching Trump.”

He argued in the trial that abuse of power is too vague to impeach a president for because it doesn’t match up to the criminal code.

Kenneth Starr, former independent counsel: He led a years-long investigation into Clinton that started as an investigation into a land deal and culminated with an explicit, detailed telling of the president’s sexual affair with intern Monica Lewinsky and allegations that he lied to a grand jury and committed perjury. It was a controversial report, but it led to Clinton’s impeachment by the Republican-controlled House and his acquittal by the Republican-controlled Senate.

Despite his controversial history prosecuting a president, Starr argued in the trial that impeachment is a dangerous slippery slope that Congress should avoid when the nation is divided.

Acting White House Chief of Staff Mick Mulvaney, left, Secretary of State Mike Pompeo and White House Counsel Pat Cipollone. (Jabin Botsford / The Washington Post)

The trial’s impact on the 2020 reelection and Trump’s future

The likelihood of Trump being convicted

It is low. It would take 20 Senate Republicans to join all Senate Democrats to vote to remove him from office. So far, no Republican has said Trump’s actions are impeachable. And 38 have already said before the start of the trial that Trump should not be convicted and removed from office. If those senators hold, that leaves just 62 senators potentially voting to convict, which does not meet the 67 vote requirement.

Okay, but what happens if Trump is convicted?

The Constitution says he must be immediately removed from office. But there are no restrictions on whether he can run for office again. To prevent him from doing that, the Senate would have to take a second vote and approve banning him from public office ever again by a simple majority.

How impeachment could affect Trump’s reelection chances

It’s not clear. Even if the Senate acquits him, could Democrats’ allegations of wrongdoing be difficult for him to shake off? Or will it bolster public opinion because Trump has convinced voters he’s being unfairly treated? Or will none of it matter because voters’ opinions of him are already so baked in?

A new Washington Post-ABC News poll, which overlapped with the start of the Senate trial, finds that his approval rating has actually climbed to match the highest of his presidency, at 44 percent.

That seems bolstered by Americans’ approval of how he handles the economy. Americans are still split on party lines about whether Trump should be removed from office.

How this is affecting the 2020 Democratic presidential race

There are four senators running for president, and this Senate trial comes at the most inopportune imaginable time for their campaigns. In the days leading up to the first vote of the primary, the Iowa caucuses, these senators will be in Washington six days a week serving as jurors and unable to talk. Meanwhile, their opponents, like Biden and former South Bend, Ind., mayor Pete Buttigieg, will be free to campaign in Iowa.

This is likely to particularly affect Sens. Elizabeth Warren (D-Mass.) and Bernie Sanders (I-Vt.). Polling shows them among the top four who have a shot to win Iowa, but they’re not a lock. Democratic strategists have described this contest in a crowded field as “a jump ball.”

Both Sanders and Warren have acknowledged this could hurt their campaigns. Of course it matters,” Warren told Politico. “We just did a 3½-hour selfie line. Don’t tell me it doesn’t matter to do face to face.”

The Iowa caucuses are on Monday, Feb. 3. On Friday of that week, there will be a Democratic presidential debate in New Hampshire, and it’s a real possibility these senators might not make it to that either. If the trial goes on longer than two weeks, they could even miss the second voting contest, the New Hampshire primaries on Feb. 11.

How we got here

The events that led to the impeachment inquiry span years, and you can dig into them in this exhaustive timeline. Here’s a shorter recap.

Spring and summer 2019

The alleged quid pro quo

Congress and the Defense Department approve nearly $400 million in military aid to Ukraine in early 2019. Out of public view, diplomats urge Trump to meet in the Oval Office with Ukraine’s newly elected president — a meeting the Ukrainians view as an important signal to Russia. But that meeting is pushed off, and the military aid is ordered stopped by the White House. In late July, Trump speaks to Ukrainian President Volodymyr Zelensky, asking him to “do us a favor though” that includes investigating his political opponents and the Biden family.

In August, a whistleblower files a complaint about that call, alleging Trump had dangled a meeting with Zelensky in exchange for launching investigations of Biden and his son Hunter, and of a conspiracy theory about a Democratic National Committee server.

September

Impeachment inquiry is launched

The Washington Post’s editorial board writes that it had been “reliably told” that Trump was pressuring Zelensky to investigate the Bidens. The existence of the whistleblower complaint is reported by The Post and other outlets. The White House releases a rough transcript of the call with Zelensky, and the whistleblower complaint becomes public. Pelosi announces the House will conduct an impeachment inquiry into Trump to see whether his actions on Ukraine render him unfit for office.

October and November

A public investigation

The investigation is underway. It happens behind closed doors at first. Then we get dramatic public testimony by witnesses, many of whom say Trump held up an Oval Office meeting with Ukraine’s president in an attempt to get the probes he wanted. Many witnesses say they believe Trump withheld the military aid for the same reason.

Trump also blocked his top aides from complying with congressional subpoenas to testify in the investigation.

December

The vote to impeach

The House Intelligence Committee released a report on the findings of the investigation, and based on that, the Judiciary Committee wrote up the two articles of impeachment. The first article accused Trump of abusing his power by leveraging the federal government and taxpayer money for his personal and political gain, and the second accused him of obstructing the congressional inquiry into his actions on Ukraine.

The House voted on Dec. 18 to approve those articles, meaning Trump was then impeached.

Republicans who spoke in the debate leading up to the vote almost universally accused Democrats of looking for an excuse to impeach Trump, while Democrats argued that Trump’s conduct regarding Ukraine necessitated impeachment.

[The articles of impeachment against Trump, explained]

Late December into January

The hold on articles and beginning of the Senate trial

Almost immediately after Trump’s impeachment, Pelosi put the requisite Senate trial in doubt by not handing over the articles of impeachment or naming House lawmakers to prosecute the case against Trump in the Senate.

She said she wasn’t sure of the environment she’d be sending them into, which was code for: She doesn’t trust McConnell and Senate Republicans to shape a “fair” trial.

Over the holidays, Democrats explained that “fair” meant agreeing to call Trump’s top aides to testify in the trial. Around the same time, newly released White House emails showed that some of these same aides were actively working to halt Ukraine’s military assistance at Trump’s demand.

But McConnell had no intention of agreeing to call witnesses. So he waited. And he accused Democrats of playing politics with Trump’s fate as a duly elected president. By mid-January, it became clear that Democrats weren’t going to win this one, and Pelosi started the process to pass the baton to the Republican Senate. Opening arguments began Wednesday, Jan. 22.

Your frequently asked questions

(The Washington Post)

Can senators be ejected from the trial for not being impartial?

Nope. Even though they take an oath of impartiality, there’s nothing holding them to that. Nor does Roberts have any expressed power to enforce it.

Can Trump run for reelection after being acquitted?

Yes. Even though he’s impeached by the House, it’s up to the Senate to decide whether to convict him and dole out punishment. So if they decide not to convict him and not to kick him out of office, he can stay in office and run for reelection.

So why did House Democrats impeach Trump if they knew it wasn’t likely he’d be removed from office?

For the history books. He is just the third president impeached in U.S. history, regardless of what the Senate does.

If Trump is impeached, who will be president?

Vice President Pence.

What happens if Trump is convicted of one but not two articles of impeachment?

Then he’s still removed from office.

Can Roberts do anything to force witnesses?

He can be the deciding vote in a 50-50 split, some legal scholars theorize. Others theorize that in such a situation, he’d recuse himself.

Could the House impeach Trump a second time based on new evidence?

Yes, if the members wanted to do this whole thing over again — and there’s no evidence they want to.