What happens with all the leftover money in Trump campaign funds if when he loses

campaign funds can be used for future campaigns or donated to other campaigns. They can not be used to enrich oneself

Can he not say he is going to run again and rent property he owns all over the country to his "campaign'?

he will end up in jail in a new York minute if he tries that. I'm also not convinced that he won't face charges for what he has done after he is out.

I hope you're right.

so he will end up nailed if he tries. I don't think Biden's department of justice will turn a blind eye.

say about Presidential campaign funds, but they can still tie him up in knots over transactions.

From his presidential campaign and the Republican Party to pay for legal fees for him, family and company. That being what he can’t hide, there is no doubt that he will charge the GOP inflated hotel fees and office space in Washington and NYC.
The testimony of Michael Cohen telling a house committee that Trump boasted about how much money he could make from running for and being President. That needs to be in a Lincoln project ad.

I'm sure Trump will make sure it all gets spent, and as much as possible at Trump properties.

I am living for the day when we all get to see him go down hard.

Trump doesn't care about "law." He'll take the leftover money and keep it. Maybe he'll filter it through his minions like Parscale then take a kickback. Remember what happened to the extra Inauguration funds? No, because they disappeared into his pocket.