TORONTO -- The U.S. House of Representatives will vote on the impeachment of President Donald Trump Wednesday after three months of investigating his dealings with Ukraine.

The House can call for impeachment if they believe that the president is guilty of 鈥渢reason, bribery, or other high crimes and misdemeanors,鈥� according to the Constitution.

House Speaker Nancy Pelosi announced a formal impeachment inquiry back in September, following allegations that Trump held back U.S. military aid to Ukraine in order to pressure that country to investigate his potential 2020 election opponent Joe Biden.

Testimony was presented in House committee hearings and the House Judiciary Committee approved two articles of impeachment against Trump: abuse of power and obstruction of Congress.

When is the vote?

A House vote on the two articles is due Wednesday.

What happens at the vote?

A simple majority on the House floor is needed to formally impeach the president.

The current House of Representatives is made up of 233 Democrats and 197 Republicans, so the vote is likely to pass.

No Republicans have so far signalled that they will support the articles of impeachment, but a small handful of Democrats who represent GOP-leaning districts have said they may join Republicans in voting against them.

Approval would set up a 2020 trial in the Senate.

What happens in the Senate?

If Trump is impeached, the Senate will hold a trial presided over by the chief justice of the United States, to decide if he should be removed from office.

The Senate is controlled by Republicans, a fact which has been raised by some Democrats as a reason not to proceed with impeachment proceedings due to the fear that it would be unsuccessful and only bolster support for Trump.

The Democrat-controlled House will appoint a team of lawmakers to present the articles of impeachment to the Senate. Senators will listen to evidence presented by House members and vote on whether Trump is guilty of the impeachment charges presented.

A two-thirds majority is required to remove him from office. Republicans hold a majority in the chamber, making it highly unlikely that Trump would be found guilty.

The U.S. president has said he wants a full trial in the Senate because he would receive fair treatment there. White House officials are indicating they will mount a strong defense in the Senate and aim to flip the switch on Democrats.

On Sunday, Senate minority leader Chuck Schumer proposed that four White House witnesses be called, including acting chief of staff Mick Mulvaney and former national security adviser John Bolton.

Mitch McConnell, Senate majority leader, has rejected the call.

Schumer proposed that the trial begin the week of Jan. 6 and allow for as many as 126 hours of statements, testimony, questions and deliberations, suggesting a trial that could run three weeks or more.

What happens if impeachment is successful?

The president would be immediately removed from office and the vice president would take over until an election.

How often has impeachment been successful?

No sitting president has been removed from office due to impeachment, although impeachment proceedings have been brought against three different presidents.

Andrew Johnson in 1868 and Bill Clinton in 1998 both were ultimately acquitted and allowed to complete their presidential terms. Richard Nixon resigned in 1974 when impeachment proceedings were brought against him for his role in the Watergate scandal, preventing the House from impeaching him.

What is impeachment?

Impeachment is the process to remove an official and is enshrined in the U.S. Constitution. It can happen at the state or federal level.

There is no specific definition of a 鈥渉igh crime鈥� included in the Constitution, but the concept is essentially aimed at preventing corruption by high-level officials.

Although impeachment involves a trial, it鈥檚 not a criminal process, merely one to remove an official from office. Criminal charges being brought against an individual is a separate matter.

How does impeachment happen?

An individual member of the House can simply introduce an impeachment resolution like any other bill, which would then be reviewed by a committee, likely the House Judiciary Committee.

Or the House Judiciary Committee can first hold their own investigation and bring articles of impeachment against the president and present that evidence to the House.

Ultimately, the full House votes on whether or not to impeach.

With files from 麻豆传媒鈥� Alexandra Mae Jones, 麻豆传媒 Washington correspondent Richard Madan, W5鈥檚 Maya Hamovitch and The Associated Press