After the "repeal and replace" of Obamacare was defeated in the Senate (because enough GOP votes couldn't be found to take insurance away from millions of Americans), Donald Trump said he would now just allow Obamacare to "implode". But even he knows that Obamacare, while it has some problems, is not anywhere near imploding.
That's why he is now threatening to give that implosion some help. He is threatening to stop the funding for subsidies that help lower-income workers buy health insurance -- insurance they could not afford without the government subsidies. Cutting those subsidies off would seriously damage Obamacare -- making it unworkable, and causing millions of hard-working Americans to lose their health insurance.
Trump is a narcissist who hates losing -- and he is upset over failing to repeal and replace Obamacare. It is definitely a possibility that he would harm Americans in this way. But the crazy part is that (as the map above from Axios shows) the states that support Trump and Republicans the most (the reddest states) would be the states affected the most by stopping the funding for the subsidies. In the chart above, the states with the highest percentage of people getting those cost-sharing subsidies are those in the darker colors.
That means Trump would be cutting off his nose to spite his face. Would the Republicans in Congress let him do that? If they did, it could be tantamount to handing control of Congress to the Democrats in the 2018 election.