During a sit down with Finnish President Sauli Niinisto at the White House Aug. 28, President Trump spoke about his upcoming visit to Texas to assess Hurricane Harvey's damage. (The Washington Post)

President Trump said Monday that he would seek billions of dollars in assistance to rebuild Texas and Louisiana from the flooding caused by Hurricane Harvey but renewed his threat to shut down the government if Congress won’t agree to begin building a wall on the Mexican border.

Trump’s comments, delivered at a White House news conference, illustrate the political minefield he will navigate in September as he tries to draw support for disaster recovery funds but wages a bitter fight with lawmakers from both parties about whether U.S. taxpayers should finance the creation of a wall that he has long promised Mexico would fund.

“You are going to see very rapid action from Congress, certainly from the president,” Trump said, speaking to a reporter from Texas. “You are going to get your funding.”

Congress must reach a budget deal by Sept. 30 or many government operations will cease, though House Speaker Paul D. Ryan (R-Wis.) said last week that a stopgap measure was likely to pass, delaying a showdown until later in the year.

In any case, Harvey’s devastation represents a new challenge for the White House and Congress, requiring lawmakers to approve billions of dollars in recovery spending even though they haven’t agreed on much else this year. It will test whether Trump can overcome deep divisions within his own party on fiscal matters to prioritize aid, and whether he can suspend his adversarial governing style and even postpone his own agenda, notably an overhaul of the tax code.

Hurricane Harvey struck Southeast Texas as a Category 4 storm Aug. 25. Texans now face catastrophic flooding, which is expected to worsen. (Elyse Samuels,Zoeann Murphy,Whitney Leaming,Kurt Kuykendall/The Washington Post)

Trump said Monday that the need to secure aid for Harvey victims would not prompt him to stand down from threats to partially shut down the government if Congress doesn’t provide funding for a border wall. “It has nothing to do with it,” Trump said.

He did not say how he would secure the emergency funding for Texas and Louisiana. In the past, he has expressed similar confidence about passing other bills only to have the process bog down when lawmakers fought over details. One difference this time, however, is that a number of Republicans and Democrats have already expressed support for the idea of extending emergency funds to flood-ravaged areas.

AshLee Strong, a spokeswoman for Ryan, said Congress stands ready pending a formal aid request from the Trump administration. “We will help those affected by this terrible disaster,” she said.

Democrats on Monday said Congress ought to respond quickly to the growing calamity, challenging Republicans to refrain from the politicking that surrounded the aid packages offered to victims of previous major storms.

“Republicans must be ready to join Democrats in passing a timely relief bill that makes all necessary resources available through emergency spending,” House Minority Leader Nancy Pelosi (D-Calif.) said.

A senior Democratic aide said the party’s position is that emergency spending need not be offset by cuts elsewhere in the federal budget, making Pelosi’s statement a challenge to Republicans who have insisted that previous aid packages not add to the federal budget deficit.

Flooding persists as Harvey downgraded to tropical depression

When Sandy struck New Jersey and New York in 2012, conservative Republicans insisted on offsetting any new spending. So when President Barack Obama pushed for a $60 billion package of federal aid, it sparked more than three months of partisan sparring — a delay that left Democrats and northeastern Republicans fuming while the remainder of the GOP fulminated against the threat of a growing national debt and the inclusion of spending they deemed wasteful.

Texas’s Republican senators opposed the Sandy relief bill, arguing that it included extraneous spending, as did most of the GOP members of the Texas House delegation. White House budget director Mick Mulvaney, then a South Carolina congressman, opposed the bill, as did Ryan, who was serving as House Budget Committee chairman.

Raw emotions from that episode persist. Rep. Peter T. King (R-N.Y.), who fought hard to secure funds after Sandy, said over the weekend that he would support Harvey relief funds even though Sen. Ted Cruz (R-Tex.) had opposed Sandy funding.

“Ted Cruz & Texas cohorts voted vs NY/NJ aid after Sandy but I’ll vote 4 Harvey aid. NY wont abandon Texas,” King tweeted. “1 bad turn doesnt deserve another.”

Cruz, speaking Monday on MSNBC, called the criticism “political sniping” and stood by his vote against Sandy aid: “The problem with that particular bill is, it became a $50 billion bill that was filled with unrelated pork,” he said. “It’s not right for politicians to exploit a disaster when people are hurting to pay for their own political wish list.”

Democratic aides said that while they expect the party to support Harvey aid, lawmakers will not be shy about pointing out what they see as hypocrisy among GOP lawmakers who opposed aid for Sandy — which affected largely Democratic states.

“Democrats certainly don’t forget how these Republicans voted on other aid packages, that’s for sure,” one senior Democratic aide said Sunday.

Congressional sources said it could be weeks before a specific price tag for a relief bill emerges. Rep. Al Green (D-Tex.), who represents part of the Houston metropolitan area, said Monday that he has conferred with some of his Texas congressional colleagues about an emergency spending request and that he hopes political squabbles will be set aside.

“This is what the government is supposed to do — respond when there’s a crisis, provide for the safety of the public,” Green said.

The economic impact of major storms can be severe. Hurricane Katrina, in 2005, caused $160 billion in damage, and the remnants of Hurricane Sandy in 2012 caused about $70 billion in damage, according to inflation-adjusted figures provided by the federal government.

Some analysts on Monday had already begun to assess Harvey’s potential damage. JPMorgan Chase sent a note to clients saying the insured losses alone could range from $10 billion to $20 billion, hitting private companies that had sold flood coverage in the area. But the total damage is expected to be much greater than just the insured losses, as many people in the area didn’t have flood insurance, and there has been substantial damage to roads, bridges and other public infrastructure.

The federal Disaster Relief Fund administered by the Federal Emergency Management Agency had a balance of $3.8 billion at the end of July, of which $1.6 billion is already obligated, according to the most recent federal report. Trump declared Harvey a major disaster Friday, making Texas victims eligible for relief from that fund. But with damage estimates already rising into the tens of billions of dollars, the fund’s balance is almost certainly inadequate.

The White House had proposed an 11 percent cut to FEMA’s budget as a way to free up more money for the military. GOP congressional leaders had signaled they would ignore that request and keep FEMA funding basically flat, but much more will have to be appropriated to respond to Harvey.

“All of our plans on disaster recovery are premised with the federal government coming in with a big chunk of short-term FEMA money and then a big chunk of long-term bailout money,” said Edward Richards, director of the Louisiana State University Climate Change Law and Policy Project. “With the budget coming up and the debt ceiling coming up, you could easily see this getting absolutely lost in the mix.”

A related issue is the status of the National Flood Insurance Program. Its federal authorization expires Sept. 30, and it is more than $24 billion in debt. The program has a statutory borrowing limit of about $30 billion, and numerous new claims could require congressional action to ensure there is enough funding.

Directing emergency funds to areas hit by natural disasters had traditionally been quick bipartisan exercises, but that changed after Hurricane Katrina in 2005 — when the Republican Study Committee, a group of House conservatives, pushed spending cuts to compensate for the approximately $200 billion expected in Katrina relief — including cutting farm subsidies, Amtrak funding and postponing the Medicare prescription-drug bill Republicans had approved two years earlier.

The study committee’s chairman at the time was Mike Pence, who represented an Indiana House district and is now vice president. “We simply can’t allow a catastrophe of nature to become a catastrophe of debt for our children and grandchildren,” he said at the time.

In a sign that the politics of disaster relief could quickly change, Rep. Mark Walker (R-N.C.), the current chairman of the Republican Study Committee, declined to draw a hard line against approving storm relief without offsets.

“We’re not saying anything is off the table,” he said. “This is such a humanitarian crisis, and the dollar amount is unlike anything we’ve seen before. I think it’s something we’re going to have to review.”

But Walker said he understands that members will have to square their previous votes on disaster relief with their positions on Harvey aid: “As far as saying, ‘Can you explain why you wouldn’t vote here, but in this case you would?’ — I think that’s an expectation and, frankly, probably a pretty fair question.”

Ed O’Keefe contributed to this report.