President Trump weighed in this morning on the internal GOP debate over whether to try to repeal the Affordable Care Act's individual mandate as part of a tax reform bill.

Wouldn't it be great to Repeal the very unfair and unpopular Individual Mandate in ObamaCare and use those savings for further Tax Cuts.....— Donald J. Trump (@realDonaldTrump) November 1, 2017

Why it matters: This move would likely open up the exact same rifts that sunk Republicans' health care efforts earlier this year, making tax reform even harder and imperiling the party's next-best chance for a legislative victory.

What it means: According to the Congressional Budget Office, repealing the ACA's individual mandate would increase the number of uninsured Americans by about 15 million; cause premiums to rise; and save the federal government roughly $380 billion over a decade. (Because fewer people would have insurance, the government would spend less on the ACA's subsidies.)

• That's a lot of savings to help make up for the revenue the government would lose through big tax cuts.
• And the individual mandate is an unpopular part of the ACA — with voters overall, and especially with conservatives.
• But because it would come at the cost of an unstable insurance market, it'll be a hard sell for the same moderate Republicans who opposed their party's repeal-and-replace bills.