WASHINGTON — The Republican Congress returns to Capitol Hill this week increasingly uncertain that a major legislative victory is achievable in the three weeks before lawmakers leave town for their month-long summer recess.

Most immediately, Republican leaders and President Trump are under enormous pressure to approve health-care legislation – but that is only the beginning. Virtually every piece of their ambitious legislative agenda is stalled, according to multiple Republicans inside and outside of Congress.

They have made no serious progress on a budget despite looming fall deadlines to extend spending authorization and raise the debt ceiling. Promises to launch an ambitious infrastructure-building program have faded away. And the single issue with the most potential to unite Republicans – tax reform – has yet to progress beyond speeches and broad-strokes outlines.

The fallout, according to these Republicans, could be devastating in next year’s midterm elections. A demoralized Republican electorate could fail to turn out in support of lawmakers they perceive as having failed to fulfill their promises, allowing Democrats to sweep back into the House majority propelled by their own energized base.

Rep. Mark Meadows, R-N.C., chairman of the conservative House Freedom Caucus, said if Republicans cannot deliver on their promises in the coming weeks, voters “are going to start saying, ‘What difference does it make who’s in power?’ ”

“There is a real anxiety among the people that I serve on why we’re not putting more things on the president’s desk,” he said. “They’re tired of excuses.”

All told, Republicans are in danger of squandering their grasp on the White House, the Senate and the House after a decade of divided government and years of stoking a conservative base to expect major policy wins. Unable so far to secure progress on his top priorities, Trump is also bumping up against history: Every president of the modern era has been able to claim at least one signature legislative achievement before the first August recess.

Sen. Roy Blunt, R-Mo., a member of the Senate Republican leadership, said he worried that his party is not seizing the early months when a new president is historically best positioned to enact the boldest parts of his agenda.

“I think there’d be no reason for voters to look at this yet and think, ‘Oh my gosh, a lot of the most valuable time of an administration is already gone.’ But if you’ve watched this for years, when an administration really makes great successes, it’s usually in that first year – and, more importantly, in that first seven months of that first year,” he said.

A growing number of Republican leaders and lobbyists think the party must move quickly beyond health care, win or lose, and proceed with a less internally divisive tax bill. Leaders had already abandoned, back in the spring, their earlier goal of passing tax reform over the summer. But with health care consuming the Senate, they have shown few signs of progress.

“Republicans recognize they’re not out of the woods,” said Thomas Davis, a former Virginia congressman who directs Deloitte’s federal lobbying practice. Davis said he thinks the Republican victory in a special congressional election in Georgia last month granted the party a reprieve – but it won’t last long without a legislative achievement.

“They’ve got a high wave coming at them in the midterms,” he said. “I think they realize they’ve got to buckle down and do things. They’ve got to produce, and tax reform would be the number one thing.”

Key Republican leaders have started looking beyond health care. Senate Majority Leader Mitch McConnell, R-Ky., has acknowledged the possibility of a bipartisan repair to ailing health insurance markets should Republican senators fail to come to terms on a more ambitious ACA replacement. And House Speaker Paul Ryan, R-Wis., has turned his attention squarely to tax reform as the health-care legislation that barely passed his own chamber sits in the Senate.

Watching on the sidelines are Democrats, emboldened after spending weeks generating public opposition to the Republican health-care plan and whose cooperation will be needed to pass a series of complex items in the coming months.

Sen. Elizabeth Warren, D-Mass., said she’s amazed that Republicans “are willing to burn time off the congressional calendar pursuing this terrible plan when deadlines are bearing down on us, like raising the debt ceiling.”