Nothing.
Fear is the great uniter. If the gop leadership can create enough dread and enough uncertainty in the future, they believe that the weak-in-the-knees "party faithful" will once again hold their noses and vote republican.
How far will this bunch go to scare the electorate?
All politics is local, indeed.
Those so hopeful of teaching the "Republican Party a lesson" almost certainly live in a district where the GOP candidate is safe.
The party in power usually does lose a few seats in off year elections. This is normal. The key this year is to hold that loss to a minimum. The way to do that is to find the vulnerable districts and send money and volunteer your time to the GOP candidate in that district, who will certainly be more conservative than the Democrat.
And if you are an immigration zealot, that is your right. The way to blend both imperatives if to find vulnerable districts or states where the GOP House or Senate candidate shares your view and focus your money and time there.