When Trump loses the election, he will claim he was winning until this (which isn’t true) and blame a loss entirely on the infection.
He will use this as an excuse to not participate in the remaining debates, which were a debacle for him, and continue his claims that the debate commission and moderators are biased against him anyway.
On the other hand, he may know that he is losing and use this as an excuse to withdraw and claim he would have won a historic victory had he remained.
He will, of course, demand testing of Biden. Biden will oblige and test negative.
He will push for a delay of the election (which won’t go anywhere) claiming anything else is historically the most unfair thing ever in a presidential race.
If the shoe was on the other foot Trump would have immediately demanded that Biden withdraw as physically incapable.
There will be far-right rumors that Trump was infected by deep, dark state actors.