WASHINGTON — House lawmakers left Washington for their weeks long August vacation, promising to return in September to tackle tax reform and finally claim a major legislative win that has so far eluded President Donald Trump and Republicans in charge.

Senators are staying behind for a scheduled two-week stint in which they hope to clear a backlog of nominations and routine legislation that’s been put off as Republicans have struggled on health care.

When Congress returns Sept. 5, lawmakers will face have an extensive and difficult roster of must-do items, most important among them increasing the federal debt limit and, separately, preventing a government shutdown when the fiscal year ends on Sept. 30. Federal flood insurance and the popular children’s health insurance program expire as well.

Republicans are also far behind on the budget, a prerequisite for any Republican-only overhaul of the tax code. And, Congress is far behind on the annual round of spending legislation, the 12 appropriations bills that fund government agencies.

“We have so much work still to do, and the House will continue to focus on issues that are important to the American people,” House Speaker Paul Ryan, R-Wis., said, adding that he is “disappointed and frustrated” by the Senate’s botched health care effort. “At the top of that list is cutting taxes for middle class families and fixing our broken tax code.”

It’s a daunting to-do list. And for the most part, success wouldn’t bring a political pay-off. Instead, the reward is forestalling disasters such as a first-ever default on U.S. obligations and a politically bruising government shutdown.

“We’ll come back. We’ll start our tax. We’ll do our (appropriations). We’ve got a budget. We’ve got a lot of work still to do,” said House Majority Leader Kevin McCarthy, R-Calif. “We’re not going to give up on health care. We’re going to have to take a different route … once the Senate is able to wake up and realize what they did and come back to their senses.”

One obvious need is short-term spending legislation, called a continuing resolution or CR in Washington-speak, to prevent a partial government shutdown on Oct. 1. GOP leaders hope the stopgap measure will pass with ease, but it’s likely to be a vehicle to extend other expiring programs.

The stopgap spending bill would keep the government’s doors open; increasing the debt limit is required to pay obligations like interest payments on the debt, Social Security benefits, and payments to government contractors. Defaulting on such obligations could have drastic consequences for credit markets and the economy, but it’s a toxic vote for most Republicans.

Democrats largely provided the votes for recent debt increases but Trump’s victory complicates the political calculus and probably means that more Republicans are going to have to step up.

“September is going to be a very difficult month. Obviously all of this is coming into play right away,” said House Freedom Caucus Chairman Mark Meadows, R-N.C.

Meadows’ hard-right Freedom Caucus is among the players in an impasse among Republicans on the budget. The nonbinding measure, once passed by both House and Senate, can set the table for this fall’s overhaul of the nation’s tax code, allowing it to advance through the Senate without fear of a filibuster by Democrats. But conservatives are pressing for spending cuts as well, which has sparked another spitting match with GOP moderates.

House Republicans muscled through a hybrid four-bill spending measure on Thursday, giving the Pentagon a more than $70 billion budget increase over a set of budget “caps” left over from a 2011 budget deal. There’s bipartisan support to increase these so-called sequestration spending levels but to do so would require Capitol Hill GOP leaders and top Senate Democrat Charles Schumer of New York — and the Trump White House — to negotiate a new budget deal.

Schumer told reporters Friday that he’s eager to figure out a September budget pact, and hopes it will follow the bipartisan template of this spring’s wrap-up spending bill.

“No muss, no fuss. I hope the same thing will happen when we deal with the issues of budget and appropriations, and funding the government next time,” Schumer said. “And how debt ceiling plays into that, we’ll wait and see.”

First in the Senate would be a defense policy bills that’s a top priority of Arizona GOP Sen. John McCain, recently diagnosed with brain cancer. GOP leaders had hoped to smooth passage of the measure next week, but Sen. Rand Paul, R-Ky., objected, and McCain headed back to Arizona for treatment.

A spokesman for Paul, Sergio Gor, said the senator wanted consideration of two amendments, one on ending indefinite detention and the other on the authorization of the use of military force. Paul planned to work with leadership on securing action on his measures.

“We’re looking at a whole lot of work,” said Rep. Doug Collins, R-Ga. “We’re going to have to get in and bear down and I hope the members are aware of that when we get back.”