I'll excuse you because you don't live in SE Texas. But DeLay has certainly been very negative on Campbell. Link Furthermore, the DeLay campaign has said that unless a voter belongs to a local GOP organization and votes in every single primary, that voter is "nothing more than an outsider who isn't concerned with conservative issues or fighting for the priorities of Texas taxpayers". I observed at the time that that was not wise.
and Campbell has no hardcore constituency to be alienated.
Then why are you thinking there might be a runoff?
With a low voter turnout expected, anything can happen. Let's say just six percent of the registered voters support Campbell, but they all turn out to vote for him.
That would be close to an outright victory for Campbell, and certainly would force a runoff if voter turnout is 13% as predicted.
You and I arguing about it isn't going to change what will happen on Tuesday. Heck, I suspect half of those casting ballots have already voted. I have.