Comparing his verbal hiccups to Palin's outright disregard for language is an apple-to-orange affair.
The "misunderestimate" example was clearly a case of Bush starting to say "misunderstood" but meaning to say "underestimate" and not bothering to take the time and pause to let his brain catch up with his mouth. This basically describes all Bushisms: he's not actually making up words, he's just not letting them come out his mouth one at a time.
Sarah's "refudiate" is a word she thinks is real. This is dumb. Real dumb. George W. Bush wasn't this dumb.
GEORGE W. BUSH WASN'T THIS DUMB. Wow, I can't believe I would ever say that.
I'm honestly not defending her but refudiate seems to work on the same level as misunderestimate. Misunderstood + underestimate/ refute + repudiate.
The verbal amalgamation is functioning essentially the same.
Sadly, if we don't make an effort to move in the opposite direction, this is how the English language will degrade throughout society as well. It's basically white people's ebonics.
Allow me to defend neither of them and slag George for a second. True, many of his Bushisms can be chalked up to flustering, but there are still ones like "the problem with the French" that aren't explained away by that.