WASHINGTON: US lawmakers will vote Thursday to repeal and replace Obamacare, Republican House leaders said, in the latest effort to provide President Donald Trump a crucial legislative victory in his first months in office.

The announcement comes after a new health care reform bill gained momentum Wednesday when two key Republican representatives -- Fred Upton of Michigan and Billy Long of Missouri -- reversed course and threw their support behind the measure following intense lobbying by the president himself.

"We will be voting on the health care bill tomorrow. Because we have enough votes," Majority Leader Kevin McCarthy told reporters late Wednesday.  "It´ll pass. It´s a good bill."

The vote, which follows weeks of tweaking to the controversial bill in order to bring enough Republicans on board, is expected to be very close.

With no Democrats supporting the revision, Republicans will need to cobble together the 216 votes necessary to pass the legislation exclusively within their own party, despite internal differences on the way forward. They can afford just 22 defectors.

The effort to repeal and replace the Affordable Care Act has been seven years in the making. Republicans including Trump have campaigned relentlessly on pledges to dismantle Obamacare.

An earlier version of the Republican plan collapsed in March, when opposition from both moderates and conservatives torpedoed their own party´s attempt to do away with former president Barack Obama´s Affordable Care Act of 2010.

But leadership apparently won over enough skeptical members with an amendment drafted by Upton which adds $8 billion to help cover insurance costs for people with pre-existing conditions.

Trump has touted the amended draft multiple times in recent days, and engaged personally in the arm-twisting, reaching out to several Republicans by phone and in person.

"The president said ´Billy we really need you. We need you, man.´ I said ´You don´t have me,´" Long told reporters at the White House, describing an extended back-and-forth with Trump over what it would take for Long to back the bill.

Long says he jumped on board after the president gave his blessing to the amendment that adds the supplemental $8 billion, which would bu used to cover health care costs for people in so-called "high-risk pools" that

Upton previously opposed the legislation, saying he was uncomfortable with a provision allowing states to remove coverage guarantees for people with pre-existing conditions -- guarantees that were provided under Obamacare.

Many health policy experts and Democrats, however, say $8 billion will not be enough to help provide coverage for sick people.

"This craven bill is going to hurt many, many more Americans," Democratic Senator Cory Booker told MSNBC.

The bill faces a steeper path in the Senate, where Republican moderates are almost certain to change the legislation, a move that would prompt a new round of negotiations.