House Speaker Mike Johnson is overseeing one of the smallest House majorities in history as Congress confronts upcoming battles over government funding and contentious fights over immigration and impeachment.

Republicans currently control just 219 seats while Democrats control 213 after Ohio GOP Rep. Bill Johnson resigned from Congress earlier this month to take a job as president of Youngstown State University.

The razor-thin majority presents an enormous challenge for the speaker, leaving him with almost no room for error as he navigates demands from competing wings of his party.

There are currently three vacancies in the House following Johnson’s departure, former Speaker Kevin McCarthy’s resignation from Congress at the end of last year and the expulsion of former GOP Rep. George Santos of New York.

Democratic Rep. Brian Higgins of New York has also announced plans to leave Congress, and will be stepping down on February 2, his office told CNN.

A special election to fill the seat previously held by Santos will take place on February 13. The race is expected to be competitive and is a potential pickup opportunity for Democrats.

In addition to the tight margin, there is always the possibility that absences can further impact the vote math.

House Majority Leader Steve Scalise’s office has said that he will work remotely until returning to Washington in February as he recovers from a stem cell transplant.

Republican Rep. Hal Rogers of Kentucky was hospitalized following a car accident earlier this month. His office subsequently announced that he had progressed to physical rehabilitation to assist in his recovery.

The tight vote margin means that any individual member has the potential to exert outsized influence and Johnson has frequently felt pressure from his right flank.

Hardline conservatives have already shown that they can hold major sway in the chamber with such a narrow majority – most notably when a group of hardliners moved to oust McCarthy from the speakership in a historic and unprecedented vote last year.

The exact size and scope of the far right of the House Republican Conference can vary from issue to issue. A contingent of roughly a dozen hardliners staged a rebellion on the House floor earlier this month, taking down a procedural vote to show opposition to a spending deal Johnson had reached with Senate Majority Leader Chuck Schumer.

The ever-shrinking margin has forced Johnson to put bills directly onto the floor under a procedural move known as suspension of the rules in certain instances as his right flank has increasingly taken to tanking rule votes on the floor in a show of protest, a dynamic that will likely continue and may intensify.

But that strategy compels the need for a two-thirds majority to pass bills, requiring significant Democratic support, and further alienating Johnson and the right wing of his conference.

In one recent example, the House passed a short-term funding extension to avert a shutdown under suspension of the rules earlier this month. House Republicans were nearly evenly divided in the vote, a sign of the deep rift within the conference. One hundred and seven Republicans voted for the bill, while 106 voted against it. Far more Democrats than Republicans voted for the measure with 207 Democrats in favor and just two opposed.

In addition to facing pressure from conservatives, Johnson must also balance the interests of more moderate members from battleground districts who are on the frontlines of the majority and who will be under intense scrutiny during the 2024 election year.

There were 18 Republicans in House districts that President Joe Biden won in 2020 – a number that is now down to 17 after the expulsion of Santos. The fate of these politically vulnerable members will be key to whether the GOP can hold onto its majority.