After a halting start, the Republican-controlled 115th Congress — sometimes in collaboration with President Trump, often despite him — has enacted surprisingly far-reaching conservative achievements in its first year, among them a long-promised rewrite of the tax code, oil drilling in the Arctic and a series of lifetime appointments to the judiciary.

For the new year, Republican leaders in the House have their sights on decades-old programs for the poor that they say are too easily exploited by those who do not need them. Mr. Trump will move forward with a long-promised program to rebuild roads, bridges and other infrastructure.

And Senator Mitch McConnell of Kentucky, the Republican leader, is speaking gamely of bipartisanship, especially on legislation to protect young undocumented immigrants brought to the country as children, whose Obama-era protection from deportation will run out in March.