WASHINGTON — In swamping large swaths of Texas and Louisiana, Hurricane Harvey also forged a new reality for President Trump and the Republicans governing Washington.

Gone are the confrontational talk of a government shutdown and the brinkmanship over the debt limit. Instead, both Mr. Trump and his putative allies in Congress — many of them professed fiscal hawks — are promising an outpouring of federal aid to begin a recovery and rebuilding effort that will last for years and require tens of billions of dollars, if not substantially more, from Washington.

The storm has utterly transformed the federal fiscal picture.

“This is going to change the whole dynamic for September and, quite frankly, for the Republican establishment for the remainder of the 115th Congress,” said G. William Hoagland, a longtime chief budget adviser to Senate Republicans who is now a senior vice president at the Bipartisan Policy Center. “The truth of the matter is, they don’t need money to build a wall in Texas, but to rebuild the shoreline in Texas.”

Facing a difficult September, deeply divided over spending and what to do about the debt limit, Mr. Trump and congressional leaders may find that a devastating storm has provided them the common cause that has proved so elusive after their failure to repeal and replace the Affordable Care Act.