House Republicans’ starting majority has now been cemented at 220 votes, with Democratic Rep.-elect Adam Gray formally ousting GOP Rep. John Duarte as of Tuesday night. That’s already an incredibly thin margin, but it’s going to get slimmer.

After some of President-elect Donald Trump’s expected nominees leave the House, Speaker Mike Johnson is expected to have literally no wiggle room, right as Republicans embark on an ambitious agenda to pass a sweeping party-line package on energy, immigration and defense policy within the first 30 days of the Trump administration. And they plan to follow that up with another partisan bill on taxes and other priorities.

If Johnson’s members leave before the votes on those bills, he wouldn’t be able to lose a single vote at full House attendance.

Let’s math: Start with the official 220-seat Republican and 215-seat Democratic majority. It’s already a mirage, because former Rep. Matt Gaetz (R-Fla.) has said he won’t return for the 119th Congress. So that drops to 219 GOP seats.

Then you have more swift exits coming. Rep. Elise Stefanik (R-N.Y.) is expected to be quickly confirmed to be ambassador to the United Nations, dropping that to 218 Republican seats.

Ditto Rep. Michael Waltz (R-Fla.), who’s joining Trump’s Cabinet in a role that does not require Senate confirmation. So make that 217 GOP-held seats.

There’s your actual margin: 217-215, Republicans hold the chamber. And remember, if it’s a tie vote, the legislation doesn’t pass — so Johnson can’t afford to lose a single Republican if Democrats unanimously oppose measures on the floor.

We looked previously at some of the possible blocs of headaches Johnson will face as he gets into the season of nuts and bolts legislating — with his and Trump’s agenda in the balance. Republicans are vowing strong unity this go around, but that’s going to be incredibly tough when just one House member can delay or derail legislation.