Foreign aid is actually extremely unpopular in the US. Even a majority of Democrats don't support it.

I would suggest that is likely because not enough Americans understand how foreign aid benefits the US. They likely think it's a hand-out or charity. It's not. It's multi-faceted, designed to help the US exert it's influence but also to help promote stability and new markets. The US economy thrives when there is a stable world market. The Marshall Plan wasn't altruistic charity. Yes it was in part an effort to thwart communist influence - but more than anything it was recognition that the US economy would only thrive with strong global trading partners and it helped make Europe reliant on US industry. The speedy restoration of Europe was probably the single greatest investment the US could have made for its own economy. So yes, foreign aid is also used to create markets for US companies and for US products.

So sure, the US can withdraw it's international aid. China will be very happy to fill the gap. China has been increasing it's global aid year on year and now spends more than the US in gaining influence around the world. So while the US withdraws aid, withdraws from global trade deals, withdraws from contributing to global bodies, who do you think will benefit the most from that long term?

If the foreign aid they're getting isn't going to encourage them to do what Trump wants then it isn't doing any good for Trump anyway so he'll take it away.

So this is like Trump saying "well, if the Federal Reserve doesn't give me the exchange rates I want, I think we should get rid of it." The essence of the problem now is that Trump has zero understanding of how global trade works and zero understanding of how foreign aid works - so trying to make sense of his decisions when they have no connection to real understanding is in itself a nonsensical exercise.