By Kristina Peterson, Siobhan Hughes and Natalie Andrews 

WASHINGTON -- The GOP plan to replace the Affordable Care Act, backed by President Donald Trump and House Speaker Paul Ryan, remained in jeopardy Wednesday after a day of intense negotiations among Republicans, but the prospect of a last-minute deal showed signs of bringing many of the holdouts on board.

Ahead of a planned vote by the House on Thursday, Mr. Trump and Vice President Mike Pence, as well as other senior administration officials, huddled with lawmakers through the day on proposed changes to the bill, aiming in particular to win support from a bloc of conservatives.

But it wasn't until Wednesday night that the outlines of a deal emerged that had potential to secure passage of one of the party's central policy goals, replacing the law known as Obamacare.

GOP leaders were exploring whether they could repeal the ACA's requirement that insurance policies cover 10 specific benefit categories, known as essential health benefits. Those include maternity care, certain pediatric and mental-health services and preventive health services. Some Republicans believe the requirement has driven up premiums, while Democrats say it ensures that plans truly cover needed services.

"We're encouraged tonight at the real willingness of not only the White House but our leadership to make this bill better," said Rep. Mark Meadows (R., N.C.), who leads a group of 30 to 40 conservatives called the House Freedom Caucus, many of whom have said the bill doesn't go far enough in wiping away the 2010 health law championed by Democrats.

It was the most optimistic assessment from Mr. Meadows in recent days. But he cautioned: "We're not there yet."

Mr. Trump called Mr. Meadows on Wednesday night during a meeting of the caucus to discuss the latest proposed changes, aiming to urge the process along. "We're very optimistic that if we work around the clock between now and noon tomorrow that we're going to be able to hopefully find some common ground," Mr. Meadows said.

Other conservative lawmakers also left the caucus meeting optimistic.

"Most good things happen toward the end of the discussion," said Rep. Trent Franks (R., Ariz.).

House leaders haven't yet decided whether to make the change to the bill, and thee proposal was still under negotiation. Its reception among more centrist Republicans, some of whom are also wary of the bill, remained unclear, and the measure threatened to significantly complicate the bill's passage in the Senate.

Until Wednesday night, House GOP leaders had warned conservatives that eliminating the coverage requirements in the House bill would risk stripping it of its special procedural status when it goes to the Senate. Republicans are using a procedural shortcut that would enable them to pass the bill in the Senate with only GOP votes, requiring a simple majority, rather than the 60 votes that most legislation needs in the Senate. Republicans hold 52 seats in the chamber.

"What we just don't want to do is put in a 'fatal provision,' " Mr. Ryan had said Wednesday morning on a Wisconsin radio show.

But by the evening, House GOP leaders said they received new advice from Senate Republicans: While the change might not survive in the Senate, it wouldn't enable Democrats to block the whole bill, a GOP leadership aide said.

About 30 House Republicans had remained opposed to the bill earlier in the day, a survey of House GOP members by The Wall Street Journal found. GOP leaders can lose no more than 22 Republican votes, since no Democrats are expected to support the bill.

The bill would dismantle much of the ACA's taxes and subsidies, and replace them with tax credits largely tied to age, aimed at helping people afford insurance if they don't get it through employers.

If insurers were no longer required to offer the set of mandated benefits in their plans, costs likely would rise for sicker and older people, who are more likely to want generous policies with comprehensive coverage. Younger, healthier consumers would be more likely to purchase the new, less-comprehensive health plans.

Senate Democrats said Wednesday night that Republicans wouldn't be able to retain the provision eliminating those benefits if the bill made it to the Senate.

"It will require 60 votes to repeal these protections, and the votes just aren't there in the Senate," said Matt House, spokesman for Senate Minority Leader Chuck Schumer (D., N.Y.). "It speaks volumes about the Republican Party that they need to try to make this bill worse for the American people in order to buy off the Freedom Caucus."

Also unclear was how the new proposal would affect the votes of centrist Republicans in the House, some of whom want the bill to offer more generous help to older and low-income people to help them afford insurance.

House Republicans voted nearly 90 times to repeal parts of President Barack Obama's 2010 health-care law while he was in office. But with a Republican in the White House and the prospect of a repeal becoming law, the party struggled to bridge longstanding differences over the government's role in health care.

Failure to pass the health plan would be "a big blow to the president, who is 100% behind this bill," said Rep. Tom Cole (R., Okla.). "It would obviously be a terrific setback for our leadership, and it's a big blow to Republican confidence." Defeat for the bill would also damage the prestige of Mr. Ryan, one of its main promoters.

GOP aides said there was no strategy in place for what would happen if the bill fails on the House floor Thursday.

"There is no Plan B," White House press secretary Sean Spicer said Wednesday. "There's a Plan A and a Plan A. We're going to get this done."

However, some Conservative interest groups remained strongly opposed to GOP bill. Organizations backed by billionaire industrialists Charles and David Koch said late Wednesday that they would spend millions of dollars to defeat the health-care bill, the Associated Press reported.

--Stephanie Armour and Louise Radnofsky contributed to this article.

Write to Kristina Peterson at kristina.peterson@wsj.com, Siobhan Hughes at siobhan.hughes@wsj.com and Natalie Andrews at Natalie.Andrews@wsj.com

(END) Dow Jones Newswires

March 22, 2017 22:57 ET (02:57 GMT)

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