On Thursday, President Trump — who once accused former President Barack Obama of "constantly issuing executive orders that are major power grabs of authority" — will sign an executive order to unwind parts of the Affordable Care Act. Trump has said he is furious that congressional Republicans have been unable to "repeal and replace" ObamaCare, and he promised on Tuesday to use "the power of the pen" to do something about health care. The executive order on Thursday will tell federal agencies, notably the Labor Department, to relax rules on coverage and benefits under certain plans.

The order will mostly affect smaller business and possibly individuals who band together to buy insurance as an association, short-term insurance plans, and rules on how tax-free employer-funded accounts can be spent. The cumulative goal is to leave consumers with more options, including lower-cost plans that don't cover as much. Health-insurance experts and some state insurance commissioners warn that those changes will likely undermine the federal markets more than Trump already has, in such a way that insurance could become prohibitively expensive for older and sicker people, including those with pre-existing conditions.

The association health plans and short-term plans are largely exempt from ACA rules, and expanding their reach will essentially divide the market into healthy and sick pools, says Rebecca Owen at the Society of Actuaries, adding that association health plans "have had a pretty spotty record," with some failing due to insufficient financial reserves and others accused of misleading members about benefits. "The specific steps included in the order will represent only the first moves in his White House's effort to strike parts of the law," two senior White House officials tell The Wall Street Journal, adding that they don't think the rule changes can be challenged in court. Peter Weber