By Susan Cornwell

WASHINGTON (Reuters) – House Republicans were making headway in efforts to build support for a reworked plan to overhaul the U.S. healthcare system, but have not decided when to vote, House Speaker Paul Ryan said on Thursday.

Ryan spoke as Republican leaders scoured the U.S. Capitol in search of centrist Republican backing for the amended measure after it gained the approval on Wednesday of a group of hard-right Republican conservatives who had helped to sink the original version last month.

“We’re making very good progress,” Ryan told reporters at a news conference, saying the changes endorsed by conservative Freedom Caucus Republicans on Wednesday would also appeal to moderate Republicans.

The House could vote as early as this week on the legislation, aides said, meaning it could pass the House in time for President Donald Trump’s 100th day in office on Saturday.

It remained unclear whether the amended bill could attract the 216 votes needed to pass the House, given the united Democratic opposition. Its future is further clouded in the Senate.

“We’re going to go when we have the votes,” Ryan said.

Republicans in Congress have made repealing and replacing the Affordable Care Act, commonly known as Obamacare, a central campaign promise for seven years. Republican President Donald Trump made it a top campaign promise.

But House Republicans are not keen to repeat last month’s debacle, when their leaders acquiesced to Trump’s demand for a floor vote on the bill, only to unceremoniously yank the measure after determining it could not pass.

The Republican healthcare bill would replace Obamacare’s income-based tax credit with an age-based credit, roll back an expansion of the Medicaid government health insurance program for the poor and repeal most Obamacare taxes.

The nonpartisan Congressional Budget Office had estimated 24 million fewer people would have insurance under the original version.

The new amendment that has won over a number of conservatives, drafted by Representative Tom MacArthur, would allow states to seek federal waivers to opt out of some of the law’s provisions. That includes the highly popular provision mandating that insurers charge those with pre-existing conditions the same as healthy consumers, and that insurers cover so-called essential health benefits, such as maternity care.

Some centrists say the changes do not address their worries that the bill would hurt poor Americans in the Medicaid program. Others, including Republican Representative Dan Donovan of New York, said the loosening of protections for people with pre-existing medical conditions was a major problem.

“It’s going to cost people with pre-existing conditions even more money to have coverage … It’s something that we shouldn’t be doing,” Donovan said on CNN.

House Democrats on Thursday threatened to oppose a short-term government funding bill if the Republicans try to bring the healthcare bill to the floor this week.

Ryan brushed off this threat, even though Republicans are expected to need some Democratic votes to pass the funding bill.

House Democratic Leader Nancy Pelosi told reporters that Trump was making Republicans “walk the plank” on a healthcare bill that was “wildly unpopular.”

Ryan dismissed the idea that some Republican lawmakers’ House seats were at risk if they vote for the healthcare bill. “I think people’s seats are at risk if we don’t do what we said we would do” and repeal Obamacare, he said.

(Reporting by Susan Cornwell and Susan Heavey; Additional reporting by Amanda Becker and Will Dunham; Editing by Jeffrey Benkoe)