Perry's never been all that popular among Texas Republicans, and Ron Paul has not only never run for statewide office, he's viewed as being a little fringey, which probably hurt his son's numbers.
Rand Paul’s wheels are coming off his image, as he continues to move left.
http://dailycaller.com/2011/09/22/conservative-ire-with-perry-runs-deep-reflects-racial-politics/
Ron Paul supporting Dewhurst probably won’t help Rand.
Rand’s amnesty peddling probably hurt him in Texas and many other states. Huckabee could win Iowa, Cruz wins Texas and Jeb wins Florida. Now he has to win to other states where amnesty is not popular anyway. Amnesty didn’t work for Gingrich.
Another thing that happened is the Todd Staples-Jerry Patterson Texas Amnesty solution is gone.