What is a 'motion to vacate' -- a key sticking point in GOP speaker battle?

House Republican leader Kevin McCarthy has offered a slate of concessions to rebels blocking his bid for the speakership, including making it easier to oust the speaker.

A "motion to vacate the chair" is a procedure rank-and-file lawmakers can use to remove the speaker. Current GOP rules allow for a majority of House Republicans to trigger the effort.

McCarthy had previously agreed to drop the threshold to just five lawmakers to set the procedure in motion, but as he struggles to get the support needed, he agreed to allow just one member to launch a vote -- a decision some Republicans have said could make the speaker toothless.

Here's what you need to know on the procedure.

How would it work?

A member would have to introduce the resolution on the floor. If they introduce it as a "privileged" resolution, it would force the House to take it up at some point.

Most likely, there wouldn't be a quick up-or-down vote on removing the speaker. It could be delayed for a certain period of time, and there could be a number of procedural votes as well -- on whether to refer it to a committee or on whether it is considered appropriate.

If it does come to the floor for a vote, the motion needs a simple majority to pass. Thus, if all members are present and voting, it would need just 218 votes to pass in this Congress, the same number of votes McCarthy needs to become Speaker of the House.

What about Democrats?

Clearly Democrats are loathe to throw McCarthy a lifeline in his bid to become speaker, but it's not clear how they would handle an effort to remove the gavel from his hands.

If Democrats did vote to remove the speaker, that would give McCarthy a cushion of four votes. He would be removed if five or more Republicans voted with all Democrats.

However, the last time this came up, in 2015, Democrats signaled they wouldn't go along with any plan to remove then-Speaker John Boehner, R-Ohio, largely because they feared a more conservative speaker would emerge.

The history

The motion has only been used once in American history. In 1910, an unsuccessful push to vacate the chair ultimately led to a series of procedural votes that ended up weakening then-Speaker Joseph Cannon, R-Ill.

The little-known procedural move was discussed in GOP circles in the late 1990's when frustration was building with then-Speaker Newt Gingrich, R-Ga. But it was revived on Capitol Hill in 2015 by a backbench congressman with a bone to pick with GOP leaders.

Then-Rep. Mark Meadows, R-N.C., filed a motion to vacate the chair against Boehner on July 28, 2015. Boehner ultimately resigned amid the GOP mutiny.