Rush was no Trumpster he trashed all the Trump callers in the beginning. I believe he pointed out why Trump was popular in an attempt to get Cruz or Rubio to adopt some of Trump's popular issues, but they either didn't get it or were prevented from getting it.
If you had been able to see Rush's ditto cam when he talked to Trumpettes there is no way you would believe he was pro Trump.
Once again...Rush doesn’t endorse anybody before the end of the primaries...