President-elect Donald J. Trump demanded on Tuesday that Congress immediately repeal the Affordable Care Act and pass another health law quickly. His remarks put Republicans in the nearly impossible position of having only weeks to replace a health law that took nearly two years to pass.

“We have to get to business,” Mr. Trump told The New York Times in a telephone interview. “Obamacare has been a catastrophic event.”

Mr. Trump appeared to be unclear both about the timing of already scheduled votes in Congress and about the difficulty of his demand — a repeal vote “probably some time next week” and a replacement “very quickly or simultaneously, very shortly thereafter.”

But he was clear on one point: Plans by congressional Republicans to repeal the health law now, then take years to create and implement a replacement law are unacceptable to the incoming president.