Sen. Lamar Alexander (R-Tenn.), chairman of the Senate Health, Education, Labor, and Pensions Committee, and Sen. Patty Murray (D-Wash.), the committee’s ranking minority party member, are holding four hearings on the Affordable Care Act this month. (Alex Brandon/AP)

After years of high-wattage partisan feuding over the Affordable Care Act, a Senate committee on Wednesday is holding the first in a series of hearings to try to build momentum for lawmakers to agree on some ways to strengthen the law’s insurance marketplaces.

Four hearings being held by the Senate’s Health, Education, Labor and Pensions Committee are part of a push by the panel’s top Republican and Democrat, who are racing to negotiate an agreement before the month ends. At the moment, however, the parties differ on specifics, and it remains uncertain whether any accord — even a narrow one — is possible.

This circumscribed effort follows Senate Republicans’ dramatic failure in late July to overturn central parts of the ACA. The new effort may yield a practical bipartisan response acknowledging that the insurance exchanges — conduits to medical coverage for about 10 million Americans — will continue to exist. Or it could provide another piece of evidence that the ACA is so politically toxic that compromise on it eludes even the senators most open to collaboration on health policy.

“I’m optimistic, though all of this is a lot of hard work,” “said Sen. Margaret Wood Hassan (D-N.H.), a committee member and one of several former governors working for an agreement.

According to senators, their aides and outside health-policy experts close to the negotiations, both Chairman Lamar Alexander (R-Tenn.) and Patty Murray (Wash.), the panel’s ranking Democrat, are eager to write into law federal funding of “cost-sharing reduction” subsidies. These payments to insurers offset discounts that the ACA requires health plans to give lower-income customers for annual deductibles and other out-of-pocket expenses.

The once-obscure subsidies, which President Trump has threatened to end, have emerged as a significant issue in recent months. Some insurance companies plan to raise their rates substantially for next year unless the payments are guaranteed, and others have withdrawn from ACA marketplaces in part because the payments’ future has been so uncertain.

The committee’s leaders agree that preserving the payments is important, but they differ on their duration. Alexander said in a statement that the government should promise to continue them “for another year,” while Murray said she is seeking “a multiyear agreement.”

Alexander said he is working toward “a limited, bipartisan, simple piece of legislation” that also would give states greater flexibility to deviate from the ACA’s basic rules. In particular, he and other Republicans want states to be able to let insurers sell policies that exclude some of the “essential health benefits” required by the 2010 law — an idea that is anathema to Democrats.

On the other hand, Murray and Senate Minority Leader Charles E. Schumer (D-N.Y.) want to re-create a pool of “reinsurance” money for health plans that existed during the first three years of the ACA marketplaces. This funding would help defray the cost of insuring customers with especially costly medical conditions — an idea that Republicans oppose.

Alexander and Murray consulted with colleagues over the August recess, but neither has revealed the concessions being expected from the other party. “We don’t know yet what Lamar has in mind in terms of greater flexibility,” said Sen. Angus King (I-Maine), who was planning to confer with the chairman again Tuesday evening.

Given the gap in ideas, “we are going to have the hearings, and that’s it,” said one former senior Republican congressional staffer.

Dan Mendelson, president of Avalere Health, a Washington-based consulting firm, said “the watchword for this effort is de-escalation.” With Congress’s attention focused on issues such as the federal debt limit, funding for Hurricane Harvey recovery and GOP tax plans, he said the greatest chance for improving the ACA’s marketplaces will be if a few provisions from the Senate committee are slipped without fanfare into a larger spending bill.

Democrats believe that the GOP will take a political hit if Congress fails to produce an agreement to improve the marketplaces. A new survey by the Democratic polling firm Hart Research, conducted for the pro-ACA group Protect Our Care Campaign, found that voters disapprove of the way Trump is handling health care, 61 percent to 39 percent, and sharply disapprove of GOP lawmakers’ approach, 80 percent to 20 percent.

Regardless of the negotiations’ fate, the upcoming hearings mark the closest collaboration between Republicans and Democrats in years on an issue that has defined their ideological differences perhaps more than any other.

Every morning before each of the four hearings this week and next, the committee is hosting off-the-record coffees to which all members are invited. Senate aides said the idea behind the sessions is to foster a collegial and frank discussion about what could be done to bolster the marketplaces.

The first two hearings feature two constituencies at the state level that have been centrally involved in how the ACA’s exchanges, intended for individuals and families without access to affordable health benefits through jobs, are working in practice.

Wednesday’s hearing will focus on five insurance commissioners from GOP- and Democratic-led states, while a hearing on Thursday will focus on three Republican and two Democratic governors.