U.S. President Donald Trump spent much of the year seething as his Republican allies in Congress failed to pass legislation to repeal and replace the Affordable Care Act, as Trump had promised during his campaign. On Thursday, he took a flurry of steps that he said were meant to replace "piece by piece" what he called "a broken mess."

Democrats call his actions just the latest in a series of efforts to sabotage Obamacare, as the ACA is called. Insurers and health-care groups say Trump's moves will lead to higher costs for consumers and could potentially destabilize the marketplaces Obamacare created to serve millions of Americans. The enrollment period for next year's coverage begins Nov. 1.

1. What did Trump do Thursday?

His administration cut off a disputed subsidy to insurers that is used to help lower-income people with co-pays and other cost sharing. He also signed an executive order that tells federal agencies to consider a number of steps that to make it possible for healthy people to buy cheaper plans that provide skimpier coverage than the ACA allows. That could lead to higher costs for people who remain on regular Obamacare plans.

2. Why were the subsidies in dispute?

The ACA created the cost-sharing reduction subsidies, or CSRs, as a way to help people whose incomes are low, but not low enough to qualify for Medicaid, afford co-pays and other out-of-pocket costs. Insurance companies were told to foot more of a patient's bill and wait to be repaid with CSRs. In drafting the Affordable Care Act, Congress neglected to appropriate money for the payments, but former president Barack Obama funded them anyway. Republicans in Congress sued, saying that was illegal in the absence of an appropriation. A federal judge agreed, but Obama and, until now, Trump continued to make monthly payments as the case was appealed.

3. What will the impact of the subsidy cutoff be?

That's not clear. Any action to end the payments may face legal obstacles of its own, after seventeen states and the District of Columbia won the right in August to defend the payments in a court case. Without the subsidies, some insurers have said they'll dramatically raise premiums or pull out of the law's state-based markets. Other insurers have already dramatically raised premiums for the coming year in anticipation of possibly losing the payments.

4. Who would be most hurt if it goes into effect?

The individuals who will be hardest hit by the president's decision to cut off the cost-sharing subsidies aren't the low-income people who receive the help. Insurers are required to continue offering them lower deductibles and copays, even if the government funding ends. Instead, middle-income people who buy their own health insurance would bear the burden. About eight in 10 people in the Obamacare markets for individual coverage get assistance. They'll face higher insurance prices for 2018, because insurers can only recoup their subsidy shortfall by raising premiums.