WASHINGTON — Donald J. Trump calls for “a full repeal of Obamacare” but says that “everybody’s got to be covered.” Initially, he liked “the mandate,” a central feature of the Affordable Care Act that requires most Americans to have insurance or pay a penalty, but he backed off that position under fire from conservatives.

He would allow people who purchase insurance on the individual market to take tax deductions for their premium payments. But aides acknowledge that this tax break would not be worth much to people whose income is so low they pay little or nothing in federal income taxes. For them, Trump aides say, there would be Medicaid, which the billionaire businessman says he would not cut but would turn into a block grant to state governments.

This whipsaw of ideas is exasperating Republican experts on health care, who call his proposals an incoherent mishmash that could jeopardize coverage for millions of newly insured people. But for Mr. Trump’s campaign, such criticism appears only to bolster the candidate’s outsider status. His chief policy adviser, Sam Clovis, said Mr. Trump was running against the political establishment in Washington and was therefore not relying on advice from “traditional establishment Republican people.”

Instead, Mr. Clovis said in an interview, Mr. Trump is receiving advice on health care policy from at least half a dozen “very prominent people,” but he declined to name them. “They are not ready to have their support of the Trump campaign known,” Mr. Clovis said.