I think it hinges on their (Trump, really) confidence on winning in November. No reason to do it now if you're sure you're going to win. No reason to worry about possible repercussions in the form of lost voters if you're sure you're going to lose.
Trump's chances of winning will drastically increase with another Republican Supreme Court Justice.
The election will likely be contested. When some strategically selected counties in Florida start anulling mail-in votes the Republicans will be glad to have a person who will dispute in their favour.
