WASHINGTON (AFP, REUTERS) - President Donald Trump heaped pressure on US lawmakers Monday (July 10) to pass a health care reform Bill before Congress goes on its August recess, with Republicans teetering on the edge of a potentially major failure.

As Senators returned for work in Washington after a week off, Trump challenged fellow Republicans to make good on their signature campaign promise: repeal and replace "Obamacare," the reforms of his White House predecessor.

"I cannot imagine that Congress would dare to leave Washington without a beautiful new HealthCare Bill fully approved and ready to go!" Republican Trump wrote in a menacing early morning tweet.

The Senate and House of Representatives - which passed its own health care overhaul in May, but would need to vote on any Senate changes - will go on recess for more than five weeks beginning July 28.

Trump has made repealing and replacing the 2010 Affordable Care Act (ACA) a priority, and last month expressed confidence that the Senate Bill would be a "phenomenal" plan with "heart."

When Senate Republican leader Mitch McConnell unveiled the secretly crafted new Bill in late June it immediately faced internal dissent from conservative and moderate wings of the party, and McConnell could not muster enough support before the July 4th holiday week as he had hoped.

With Democrats united in opposition, McConnell needs the votes from 50 of the 52 Senate Republicans to get the measure passed.

But when he took the floor Monday for the first time in 11 days, he sounded no closer to corralling enough support to achieve the Republicans' long-held dream of dismantling the ACA.

"The Senate Republican conference will continue working to help these families because we believe that they deserve better than Obamacare and its years of failure," McConnell said.

During the holiday week, lawmakers returned to their districts where many faced constituents who expressed intense opposition to the plan. Polls show it to be very unpopular among voters.

The Senate draft would keep some parts of Obamacare intact, but strip away much of its funding. It also rolls back the expansion of Medicaid, the federal health care program for the poor and disabled.

The United States is the only developed industrial democracy that does not have universal health care. Almost 30 million Americans have no health insurance whatsoever, CDC data show.

At least 10 Republicans have said they would not support the Bill as written, including Senator Bill Cassidy, who told Fox News on Sunday that "clearly the draft plan is dead." Leadership is tweaking the measure, in a desperate bid to get enough Republicans on board, but Cassidy complained he has not even see the new version.

"Is the serious rewrite plan dead? I don't know. I've not seen the serious rewrite plan," he said.

Scores of protesters voiced opposition to the legislation outside Republican National Committee headquarters and at the offices of some Republican lawmakers on Monday, chanting slogans including"Trumpcare kills" and "Healthcare is a human right." USCapitol Police said 80 people were arrested.

'TIME TO MOVE ON'

Several Republican dissenters worry that the Bill could leave millions uninsured.

The non-partisan Congressional Budget Office projected that the Senate plan would swell uninsured ranks by 22 million more people by 2026 as compared to current law.

McConnell intends to unveil a revamped draft as early as Thursday, Politico reported, with a new CBO "score" due the following week.

That would leave less than two weeks before the August recess - precious little time for the biggest legislative lift of Trump's presidency to get across the finish line.

McConnell has signalled that if the repeal plan fails, a bipartisan fix of Obamacare might be needed.

Democrats have long said they are ready to work with Republican in that effort, and on Monday, Senate Minority Leader Chuck Schumer wrote McConnell urging him to cooperate on several Obamacare-connected measures introduced by Democrats.

But Schumer also needled his rivals for stumbling in their repeal-and-replace bid.

"It's time to move on from the failing Republican-only approach and start over in a bipartisan way in health care," he said.