“If you repeal the Affordable Care Act, you’ve got to have a serious way to expand coverage to replace what you have taken away,” said Gail R. Wilensky, who was the administrator of Medicare and Medicaid under President George Bush from 1990 to 1992. “There’s nothing I see in Trump’s plan that would do anything more than cover a couple million people.”

Robert Laszewski, a former insurance executive and frequent critic of the health law, called Mr. Trump’s health care proposals “a jumbled hodgepodge of old Republican ideas, randomly selected, that don’t fit together.”…

James C. Capretta, a senior fellow at the Ethics and Public Policy Center, a conservative nonprofit group, said Mr. Trump underestimated how difficult it would be to uproot a law that was now embedded in the nation’s health care system.

“It took a herculean political effort to put in place the Affordable Care Act,” said Mr. Capretta, who worked at the White House Office of Management and Budget from 2001 to 2004. “To move in a different direction, even incrementally, would take an equally herculean effort, with clear direction and a clear vision of what would come next. I just don’t see that in Trump’s vague plans to repeal the law and replace it with something beautiful and great.”