Perry's weakened among Republican voters. People who disapprove of Rick Perry because they view him as insufficiently conservative aren't gonna vote Donk.
Plus Perry has always had hyped opponents who belly-flopped in each of his gubernatorial elections.
I'm a Republican and I don't like Rick Perry, but not because he's "not conservative enough". Quite the opposite; I think he's too far-right. And most of America must agree with me, because when he was running for president, he was behind President Obama by double-digits in most of the general election polls nationally.