The Republican party is trying to separate its brand from Trump
This isn't about winning the presidency for the party anymore, they know that is gone. This is about trying to preserve Congressional power by convincing those who won't vote for Trump to still come out and vote down party. This is an almost impossible leap to make, so they have to distance themselves as quickly and as vehemently from their nominee as possible
The presidency for at least four years is gone to them.
Pretty much every model and most pundits concede the Senate is also now gone due to the Trump drag.
Now it is about not giving Democrats a 7% or so turn out advantage that would also flip the House. All the actions you see now are trying to stem that bleeding only. The other two limbs have already been amputated.
Just think, Republican party operators are dealing with the very real possibility that they become the minority in all three branches of government (Supreme Court nominations coming, too!). November can't come soon enough.