President Trump has gotten almost everything he has wanted from the Republican-controlled Congress since he took office in January.

G.O.P. lawmakers approved his nominees, sometimes despite their doubts. They ceded their power over how federal dollars are distributed, impinging on constitutional authority. And they have cheered his overhaul of the federal bureaucracy, even as he has bypassed the legislative body’s oversight of federal agencies.

But now, Mr. Trump is pressuring Republicans to fall in line behind his sprawling domestic policy bill, even though it has elements that could put their party’s hold on Congress in greater peril in next year’s midterm elections. Fiscal hawks are appalled by estimates that the bill would add at least $3.3 trillion to the country’s ballooning debt, while moderate Republicans are concerned about the steep cuts to the safety net.

Yet Mr. Trump is still getting his way — at least so far. The Senate narrowly passed the bill Tuesday, with Vice President JD Vance breaking the tie. The bill now heads back to the House, where the president can only lose three votes, and where anger among both moderates and conservatives about changes made by the Senate is running high.

Getting the bill through the House may be the biggest test yet of Mr. Trump’s second-term political power. If he gets the bill over the finish line, it will be another legislative victory and a vivid demonstration of his continuing hold over the party.

The process of driving the legislation forward has exposed deep divisions among congressional Republicans, as well as concern about the huge political risks of supporting the bill. In the end, fear of crossing Mr. Trump kept defections in the Senate to a barely manageable level.