The Senate bill replaced flat, age-based premium subsidies with subsidies based on a sliding scale, according to income. That means that some people who would have been priced out of the insurance market under the House bill — particularly poorer, older Americans, in states with expensive health care systems — would get more help buying insurance under this plan.

But the budget office didn’t think that many such people would use those comparatively more generous tax credits, because of the high deductibles. Low-income people, it said, would look at both the sticker price and the value of health insurance and tend to opt out of the market.

“As a result, despite being eligible for premium tax credits, few low-income people would purchase any plan,” the analysts said. The bill also took away financial assistance for higher-earning middle-income Americans. That change would leave an average 64-year-old earning around $55,000 with no help paying a $20,500 annual premium.

The Senate bill slowed a retreat from Medicaid expansion that was part of the Affordable Care Act. Instead of instantly slashing federal funding for that new population in 31 states in 2020, the Senate bill would step down the federal share of spending over several years. But according to the budget office, the end result is quite similar.

By the end of a decade, the budget office estimates that 15 million fewer Americans would have Medicaid coverage; that’s 1 million more than under the House bill. The Senate bill pays for the more generous Medicaid phaseout in the early years by reducing the program’s overall spending more sharply later. The budget office’s estimates span only 10 years, but its analysts noted that they expect “that after 2026, enrollment in Medicaid would continue to fall relative to what would happen under current law.”

The president has decried unstable markets under Obamacare, pointing to places that have been left with only one insurance carrier — or are at risk of none. The budget office said that the individual markets under the Senate bill would be less likely to be stable and more likely to include coverage gaps, particularly in rural areas.