UPDATE: Republicans Can’t Kill Obamacare, So They’re Turning It Into Trumpcare
Any day now, the Trump administration will unveil a proposal to change the regulation of short-duration insurance plans. These are plans that don't typically include mental health or other essential benefits the Affordable Care Act requires, and they are almost never available to people with pre-existing conditions - which means insurers can sell them for a lot less money.
Once the Affordable Care Act took effect, the Obama administration decided short-term plans would not count toward satisfying the individual mandate and that, as of this year, they could last no more than three months. As with so many other decisions the Obama administration made, this was both an effort to protect people from insurance that would leave them exposed to catastrophic medical bills as well to make sure insurers selling comprehensive, regulated plans weren't losing healthy customers to cheaper alternatives unavailable to the sick.
The Trump administration plans to alter those rules, and, although the details are not public, it's likely that the plans will officially be available for up to a year, as they were previously, and that they will count toward the mandate, if the mandate-still exists. If healthy people can buy these plans or longer than three months and can do so without incurring a financial penalty from the mandate, many more are likely to choose that option - causing insurance markets to deteriorate even more as premiums for comprehensive policies go up and more people seek out cheaper alternatives.