Rep. Mike Gallagher (R-Wisc.), the chair of the China Select Committee, said Friday he'll resign from Congress on April 19.

Why it matters: House Republicans will have a one-vote margin when Gallagher leaves, which is set to dwindle even further later in April.

• A special election to replace former Rep. Brian Higgins (D-N.Y.) is set for April 30 and is likely to send another Democrat to Congress.
• Gallagher was already planning to retire at the end of the congressional session next January.

What he's saying: "After conversations with my family, I have made the decision to resign my position as a member of the House of Representatives for Wisconsin's Eighth Congressional District, effective April 19, 2024," Gallagher said in a statement.

• Gallagher said he "worked closely with House Republican leadership on this timeline" and that his office will "continue to operate and provide constituent services" for the remainder of his term.
• Gallagher, 40, was seen as a rising star in the GOP and was pushed, unsuccessfully, to run against Sen. Tammy Baldwin (D-Wisc.) this cycle.
• Politico was first to report news of Gallagher's retirement.

By the numbers: Republicans are set to be down to just 218 members to Democrats' 213 when Rep. Ken Buck's (R-Colo.) resignation takes effect on Friday. Gallagher will bring that to 217.

• Republicans will be able to afford just one defection on any party-line vote when Gallagher leaves — any more would cause a bill to fail.
• Higgins' replacement will likely bring Democrats up to 214, but three special elections in May and June to replace Buck and other Republicans will almost certainly give Republicans some breathing room.

Between the lines: Republicans were already panicking when Buck announced his resignation, and Gallagher's departure is likely to set off a five-alarm fire.

• But House Speaker Mike Johnson (R-La.) has also essentially dispensed with party-line votes in favor of voting on major, bipartisan legislation under a process that requires bills to pass with a two-thirds majority.

Editor's note: This story has been updated with additional background.