WASHINGTON — Some Medicare beneficiaries would face higher prescription drug costs under President Donald Trump’s budget even as the sickest patients save thousands of dollars, a complex trade-off that may make it harder to sell Congress on the plan in an election year.

In budget documents, the administration said its proposals strike a balance between improving the popular “Part D” prescription benefit for the 42 million seniors enrolled, while correcting design flaws that increase program costs for taxpayers. Health and Human Services Secretary Alex Azar is expected to testify on the proposal later this week in Congress.

Trump has made bringing down drug costs a top priority, but his administration’s plan would create winners and losers. The high cost of medicines is the leading health care concern among consumers.

Independent experts said the administration’s plan will help beneficiaries with the highest prescription drug costs, an estimated 1 million of the sickest patients, those whose individual bills reach a total of more than $8,418 apiece.

But about 4.5 million seniors in the group just behind them could end up spending more of their own money. That’s because the budget proposes a change in how Medicare accounts for manufacturer discounts received by patients whose total bills range between $3,750 and $8,418. They could wind up paying about $1,000 more.