Trump is bleeding profusely from multiple self-inflicted wounds right now. There is still time for his party to stop him. The GOP, both the Establishment wing and the hard Right, can unite and declare themselves in opposition to him. They can publicly and vocally beg the American people to just not vote for him, maybe not vote for Hillary, but simply to not vote Trump, but still show up and support other Republican candidates so they can salvage as much as they can from local elections. This might save them the House, and maybe even the Senate.
With a little luck, Trump may take the hint and withdraw from the race, (I suspect he’s having second thoughts about running by now, and is desperate for an excuse to drop out and still save face.) Some other Republican, maybe even his running mate, can carry the flag for him. Even if the GOP gets crushed, or even if Trump squeezes a victory, their party honor will survive relatively intact. They can at least claim they tried to stop him. And if Hillary wins, they’ll not be totally disgraced and they can mount a credible campaign of obstruction. sabotage, blackmail and voter suppression like they did against Obama.
The GOP can then purge the last of the TPartiers out of their ranks, once and for all, and start rebuilding a more recognizable Republican Party, one not based on bigotry, redneck rage and Fascist fantasy.
Then again. They may not do anything. There’s three more months before the election. Everyone’s still waiting to see what October Surprise Wikileaks and Assange have in reserve in their quiver of poisoned arrows.