Subsidies to buy insurance from the Affordable Care Act marketplaces are set to expire at the end of 2025. If they're not extended, coverage could become unaffordable for many.
Good news, statistically a lot of them will. Republicans tend to skew older (and dumber but that's irrelevant in this case), so when he axes Medicare it's going to impact his supporters hardest.
This is the biggest part of the problem. He will do exactly that and these people will believe him because every other source on the planet is lying and only Donald Trump tells it like it is.