WASHINGTON — Speaker Mike Johnson has dropped one of the most aggressive options the GOP was considering to cut Medicaid costs to help pay for President Donald Trump’s domestic agenda, bowing to pressure from politically vulnerable Republicans and underscoring the deep party divisions imperiling the plan.

Leaving his office Tuesday night after meeting with a group of more moderate members, Johnson told reporters that House Republicans had ruled out lowering the amount the federal government pays states to care for working-age adults who became eligible for the program through the Affordable Care Act’s Medicaid expansion.

Johnson also suggested he was leaning against another way of reducing spending on Medicaid, by changing the way the federal government pays states — currently by providing a percentage of beneficiaries’ medical bills — to a flat fee per person.

“I think we’re ruling that out as well, but stay tuned,” the speaker said.

The retreat was an acknowledgment that many House Republicans viewed the ideas — both of which would create large state budget shortfalls — as politically toxic. It also underscored how difficult it will be for Johnson’s conference to find Medicaid cuts that hit the spending targets Republicans set for themselves and also win enough votes to pass.

Ultraconservative Republicans quickly vented their opposition, in a public reminder that Johnson’s efforts to stave off a revolt of mainstream lawmakers could cost him crucial support from his right flank. That could doom Trump’s vast tax and spending cut plan in the House, where the speaker can afford to lose fewer than a handful of votes.

“Well - I haven’t ruled it out,” Rep. Chip Roy, R-Texas, declared on social media after Johnson’s comments Tuesday night about abandoning the idea of cutting back on federal payments for some Medicaid beneficiaries. “It’s necessary to stop robbing from the vulnerable to fund the able-bodied.”

And as if to drive home the point of Johnson’s challenging balancing act, a group of 32 conservatives sent him a letter Wednesday insisting that they would support the reconciliation bill only if it does not add to the deficit. That means that if Republicans fail to come up with enough spending cuts, they would also have to accept a smaller tax cut to compensate.

“The deficit reduction target must be met with real, enforceable spending cuts — not budget gimmicks,” they wrote in the letter, led by Rep. Lloyd K. Smucker, R-Pa., a member of the Ways and Means Committee.

House Republicans are laboring to identify roughly $2 trillion in spending cuts to help offset the 2017 tax cuts they want to extend and the new tax cuts they want to pass in their reconciliation bill. The biggest challenge so far has centered on the Medicaid program, which provides health insurance to 72 million poor and disabled Americans.