Unquestionably the republican power brokers have already written off this election as a loss and are starting to plan for 2020.  They'll double down on their Obama pledge to make Clinton "a one term president".  But there are a few problems with that:

1.  In 2020 they'll still have the bat**** contingent of their party, the ones who voted for Tump in the primary.

2.  Their control of congress will be a lot weaker after they lose the Senate and a good chunk of the House this year.

3.  A lot of their traditional funding has fled to the dems.  Some of it won't come back (for reasons 1 and 2 above).