This thinking is just dopey. The base is much larger than the pool of moderates. And in a midterm, the chances of exciting the moderates is slim to none...
Unfortunately, the opposite is true.
There are lots of "moderates" and "independents" out there - more as the Demoncrats move further left - waiting to be picked up. The 'Pubbies are moving left to pick up these votes. If they lose "the base" thats fine - where are they going to go? They aren't gonna vote Demoncrat...