In a move that could have implications for the Republican Party's ability to pass legislation, Rep. Mike Gallagher (R-Wis.) announced his resignation effective April 19. This decision leaves the already slim House GOP majority with a one-vote margin, making it even more challenging for bills to gain approval.

Under Wisconsin law, Gallagher's seat is expected to remain vacant until January, with the November general election determining the next representative for his district. With Gallagher's departure, House Speaker Mike Johnson (R-La.) will now be able to tolerate only a single defection from his party on party-line votes.

The consequences of this narrow majority were evident as the House narrowly passed a $1.2 trillion spending bill earlier in the day. The bill's close margin serves as a reminder of the increased difficulty the GOP will face in advancing their legislative agenda.

Gallagher, who had already declared that he would not seek re-election this year, made the decision to resign after discussions with his family. Currently chairing the House Select Committee on the Chinese Communist Party, Gallagher considers departing on a "high note." He expressed his confidence in House Republican leadership and their ability to appoint a new chair to continue the panel's important work.

The Republican Party currently holds a five-seat majority, which was further diminished by the resignation of Rep. Ken Buck (R-Colo.) earlier this week. With Gallagher leaving in mid-April and Buck's departure, the margin decreases to just two Republicans able to defect on party-line votes. Once Gallagher's resignation takes effect, the margin will shrink to a precarious one vote.

The majority will narrow even further when a Democrat is elected to replace former Rep. Brian Higgins (D-N.Y.), who resigned earlier this year. The Republicans will have to wait for a Republican to be sworn in following a May runoff election, in order to regain their lost ground after former Speaker Kevin McCarthy (R-Calif.) held the seat for over a decade.

Gallagher, who has represented Wisconsin's 8th Congressional District since 2017, announced his decision in February not to seek re-election, citing the toll the lifestyle of a member of Congress takes on his young family. Previously, he drew criticism from fellow Republicans for opposing the impeachment of Homeland Security Secretary Alejandro Mayorkas.

By choosing April 19 as his resignation date, Gallagher appears to have skillfully avoided triggering a special election to fill his seat. Under Wisconsin law, special elections are held for congressional vacancies occurring before the second Tuesday in April, which falls on April 9 this year.

As the House GOP majority becomes increasingly fragile, Republicans may face considerable challenges in advancing their legislative agenda amidst a divided political landscape. The next few months will be crucial in determining the future dynamics of Congress and the fate of key legislation.