It seems highly probably that Mitt Romney will, at some point, start making that argument that Rick Perry is too extreme for America. Not merely unelectable in a general election -- that's not a winning argument in a GOP primary, apparently -- but objectively too extreme to govern the country.
We're already seeing hints of that with the debate over Social Security.
So if that happens, and if Perry nonetheless goes on to get the nomination, it's pretty much inevitable that the Obama campaign will make ads like [the one below] from 1964, in which the Johnson re-election campaign quotes George Romney [Mitt's dad] against Goldwater.
In this case, Marx had it backwards: first came the farce, then the tragedy.
Here's the video: