(Reuters) - U.S. President Donald Trump, under growing pressure from numerous investigations of him and his administration, last week scorned talk of being removed from office via the impeachment process as “dirty, filthy, disgusting.”

FILE PHOTO: U.S. President Donald Trump looks at supporters before boarding Air Force One after addressing a Trump 2020 re-election campaign rally in Montoursville, Pennsylvania, U.S. May 20, 2019. REUTERS/Carlos Barria/File Photo

The U.S. Constitution empowers Congress to impeach the president, although no president has ever been removed from office as a direct result of this arduous procedure.

Some lawmakers in the Democratic-controlled House of Representatives favor starting the process. But the Senate, where it would have to end, is controlled by Trump’s fellow Republicans. They are unlikely to remove him from office, unless public sentiment shifts strongly in favor of it.

The following is how the impeachment process works.

WHY IMPEACHMENT?

The founders of the United States created the office of the presidency and feared that its powers could be abused. So they included impeachment as a central part of the Constitution.

They gave the House “the sole power of impeachment;” the Senate, “the sole power to try all impeachments;” and the chief justice of the Supreme Court the duty of presiding over impeachment trials in the Senate.

The president, under the Constitution, can be removed from office for “treason, bribery, or other high crimes and misdemeanors.” What exactly that means is unclear. Historically, it can encompass corruption and other abuses, including trying to obstruct judicial proceedings.

Before he became president in 1974, Republican Vice President Gerald Ford said: “An impeachable offense is whatever a majority of the House of Representatives considers it to be at a given moment in history.” Ford replaced President Richard Nixon, who resigned before Congress could impeach him.

HOW DOES IT WORK?

Impeachment begins in the House, which debates and votes on whether to bring charges against the president via approval of an impeachment resolution, or “articles of impeachment,” by a simple majority of the House’s 435 members.

If the House approves such a resolution, a trial is then held in the Senate. House members act as the prosecutors; the senators as jurors; the chief justice presides. A two-thirds majority vote is required in the 100-member Senate to convict and remove a president. This has never happened.

Presidents Andrew Johnson in 1868 and Bill Clinton in 1998 were impeached by the House, but both of them stayed in office after being acquitted by the Senate.

CAN THE SUPREME COURT OVERTURN?

No. Trump has said on Twitter that he would ask the Supreme Court to intervene if Democrats tried to impeach him. But the founders explicitly rejected making a Senate conviction appealable to the federal judiciary.

PROOF OF WRONGDOING?

In a typical criminal court case, jurors are told to convict only if there is “proof beyond a reasonable doubt,” a fairly stringent standard. Impeachment proceedings are different. The House and Senate can set their own standards for proof.

PARTY BREAKDOWN IN CONGRESS?

The House has 235 Democrats, 197 Republicans and three vacant seats. As a result, the Democrats could impeach Trump with no Republican support.

In 1998, when Republicans had a House majority, the chamber voted largely along party lines to impeach Clinton, a Democrat.

The Senate now has 53 Republicans, 45 Democrats and two independents who usually vote with the Democrats. Conviction and removal of a president would require 67 votes. So, for Trump to be impeached, at least 20 Republicans and all the Democrats and independents would have to vote against him.

WHO BECOMES PRESIDENT IF TRUMP IS REMOVED?

In the unlikely event the Senate convicted Trump, Vice President Mike Pence would become president for the remainder of Trump’s term, which ends on Jan. 20, 2021.