Isn't that a dangerous strategy to take? Remember a Republican was saying a Cruz nominee would likely hurt down (can't think of a better term) tickets. Even though I still believe they would rather have Trump than Cruz, I feel Trump would hurt the party nationwide more. I don't know if there's a correlation between the performance of the presidential nominee to other tickets running.
You're right that there's a correlation, there's a reason we talk about coattails and downticket candidates tying themselves to popular presidential candidates. Cruz and Trump would both do a huge amount of damage.
Considering Republicans already have an uphill battle during presidential years damaging the brand is the last thing they want. Maybe it doesn't matter if Trump is the nominee, the appeal might already be tarnished severely. I could only see Trump acting as a catalyst.
The brand's already been damaged by Trump. Every Democrat running in November is going to try and tie their opponent to Trump somehow and it won't be too hard considering the party's stances on the issues.
At this point all the establishment can do is try and figure out a way to make sure they regain control of the party after this cycle. They didn't move fast enough so now it's a runaway train. All they can do is try and distance the party from Trump, which won't work, and minimize the damage.