He will allow the USA to become much more independent and cut off paying for other nations' wars. He will allow the USA to become much more independent and cut off paying for other nations' wars.

Kowtowing to countries like China and Russia, allowing them to win strategic victories, will make them more powerful and give them more influence on US politics. Ie. the US would become less independent.

You don't become more independent by telling countries like China that you give up.

In the case of Ukraine, they're one of the world's top exporters of grain, which is in part why food prices have been rising globally.

We don't need the rest of the world.

You do. The world has globalised. At least 40 million American jobs are directly reliant on exports. The rest of the world also produces stuff like oil. Fuel prices would skyrocket.

A lot of unprofitable stuff has also been moved overseas. It would cost money to make it in the US. Many resources are also rare in the US. Stuff like rare-earth elements. Good luck importing from countries which have signed deals with China, because they're the new super power. Combined with de-dollarisation this would also cause massive issues, rampant inflation for example. You think it's bad now? You ain't seen nothing yet.

Our military can stomp out any invaders.

No one needs to invade the US. It's cheaper to simply buy a candidate or blackmail him. This allows countries like China to push through legislation which favours their business and strategic interests. Eg. dropping support for Ukraine or dropping support of Taiwan so that China can take control of advance chip industries.

In the long term, the US would find it hard to sustain a huge military budget when facing economic turmoil and a debt crisis. Especially in relative terms. China has a population of 1.4 billion. If the US withdraws from the Asia-Pacific and Europe, they're likely to become part of the Chinese sphere of influence. A country of 300 million, will inevitably be pushed around by a power bloc of 3 billion.

Of course, none of this will convince a Trump supporter, because most base their support on emotions not reason. And once they find they can't afford to fill up on gas, or groceries, they'll blame anyone but themselves.