WASHINGTON — Projected Medicaid spending under a Senate Republican bill to repeal the Affordable Care Act would be 35 percent lower after two decades, the Congressional Budget Office said on Thursday in a new report, which detailed how Medicaid changes would cut more deeply as they go fully into force.

The budget office analysis created a fresh challenge for Republican leaders as they tried to muster support for their bill, even as senators scattered to their home states for a 10-day July 4 recess. The Senate majority leader, Mitch McConnell of Kentucky, entertained a stream of senators on Thursday, trying to reach agreement on the contents of a revised bill.

But by the end of Thursday, Mr. McConnell’s caucus still appeared far from a consensus, and it was unclear when a new version of the bill would be ready.

The nonpartisan budget office had already said that the bill would cut projected Medicaid spending 26 percent in 2026. “A large gap would grow between Medicaid spending under current law and under this bill,” the new report said, and that gap would widen, so that federal Medicaid spending in 2036 would be more than a third lower under the bill than under the Affordable Care Act.