Congress could do all sorts of things to assert its power: it could call hearings, issue subpoenas, revoke or change appropriations, pass laws, file suit, threaten impeachment, actually impeach. The courts could get involved if the administration resisted or defied some of those actions too, of course.
They have no interest in doing any of that, though. Generally those in power in Congress support what Trump is doing and are happy to have it happen without them needing to lift a finger (or take the blame if there are problems). To the extent that they don't, they're also happy to rely on the courts and again not take the blame or blowback from their voters.
As the administration plows forward and gets a taste for operating outside the law, I do think you have a growing risk that even a Congress that wanted to resist would find itself unable. You see administration figures favorably citing arguments that they should ignore court orders even now, and some evidence that they're defying orders already.
They have no interest in doing any of that, though. Generally those in power in Congress support what Trump is doing and are happy to have it happen without them needing to lift a finger (or take the blame if there are problems). To the extent that they don't, they're also happy to rely on the courts and again not take the blame or blowback from their voters.
As the administration plows forward and gets a taste for operating outside the law, I do think you have a growing risk that even a Congress that wanted to resist would find itself unable. You see administration figures favorably citing arguments that they should ignore court orders even now, and some evidence that they're defying orders already.