By Zachary B. Wolf, CNN

(CNN) -- President Donald Trump has less than two weeks left in office, but after he fomented an assault by rioters on the US Capitol, House Democrats are planning to bring an impeachment resolution -- unless Vice President Mike Pence and the Cabinet invoke the 25th Amendment to remove Trump first.

Impeaching Trump might be the appropriate remedy and using impeachment to remove him from office would bar him from running for President again. (Reminder: Trump was already impeached by the House over his Ukraine activities, but was not removed from office by the Senate.)

But impeachment takes time, and might not pass. The 25th Amendment, which has periodically been discussed as a means of last resort to remove a rogue or incapacitated president, would be a faster route to removing Trump.

Some Cabinet members held preliminary discussions about invoking the 25th Amendment to force Trump's removal from office, a GOP source told CNN's Jim Acosta last week, and Pence has not ruled it out.

But the bar it sets is incredibly high.

What would it require?

To forcibly wrest power from Trump, Pence would have to be on board, according to the text of the amendment. Read the full language here. Pence would also need either a majority of Trump's Cabinet officials to agree the President is unfit for office and temporarily seize power from him.

Trump could dispute their move with a letter to Congress. Pence and the Cabinet would then have four days to dispute him, Congress would then vote -- it requires a two-thirds supermajority, usually 67 senators and 290 House members to permanently remove him.

Congress could also appoint its own body to review the President's fitness instead of the Cabinet. House Speaker Nancy Pelosi, during the last Congress, introduced a bill to create a congressional body for this purpose, but it was not signed into law.

Why do we have the 25th Amendment?

The 25th Amendment was enacted in the wake of the assassination of John F. Kennedy, whose predecessor Dwight Eisenhower suffered major heart attacks. It was meant to create a clear line of succession and prepare for urgent contingencies.

Eisenhower suffered a debilitating heart attack while in office in the 1950s. That was before the 25th Amendment, so there was no constitutional rule. Instead he came to an agreement with Vice President Richard Nixon about handing over power.

The portion of the 25th Amendment that allows the vice president and Cabinet to remove the president had in mind a leader who was in a coma or suffered a stroke.

The Reagan administration drafted, but did not sign or transmit, letters to the Senate that would have taken power from Reagan after he was shot in 1981. You can see them at the Reagan Library's website.

The storming of the Capitol by rioters at the request of the President may end up being the first such contingency in the nation's history.

Appearing on CNN as rioters were being cleared from the Capitol, the presidential historian Douglas Brinkley said he never thought he'd seriously be discussing ousting a president who posed a danger to the Republic.

"Our country's being held hostage right now by Donald Trump," he said. "Mitch McConnell and Speaker Pelosi cannot even meet in the Capitol today ... so I think we now have to go into our constitutional kit bag and find what we can do to control Donald Trump and certainly the 25th Amendment is there."

This explainer has been updated to reflect news developments.