If he thought about it, he would reject this idea for the same reason he opposed some of the Bush tax cuts: if this move doesn't correspond with spending cuts of an equal amount, then all we are doing is wasting our time on another expensive political stunt.
Not having much else to work with, the Republican National Committee doesn't see it that way. At least not according to this email:
I can't believe they are touting agreement by Hillary Clinton on a fiscal idea as a good thing. In fact, Clinton's response indicates only that she gets the political gamesmanship:
“I would also consider a gas tax holiday, if we could make up the lost revenues from the Highway Trust Fund,” she said, without specifying how to make up those lost revenues.
Republicans won't be rebuilding much public trust with this one.