I wondered if Trump is raising money for 2020 so he can drop out and keep the cash. I wouldn’t put it past him.
If he follows the law, he can’t do that. Here’s what candidates can do with unspent funds.
Notice that one of the permitted uses is donating it to charity. Trump could donate it to the Trump Foundation , if it still exists, or a similar charity and then put it to personal use. I know that sounds cynical but look how he misspent Trump foundation money.