OTOH, should he be the GOP nominee, they can't withhold money from him. To do THAT would raise a worse firestorm than they are now under.
$2700 per individual is the max those billionaires can donate. If Trump has sworn off PAC’s and bundlers, Individual contributions is his only option unless he takes the federal funding. As for the National and State parties they can give maybe max 1 million. More than 9 million a day from small donors, it certainly will require more organization that he has displayed so far.