I had the same thought when I read the article. She needs to support Senator Thompson to remain viable to run for governor or to replace Lamar Alexander in the senate. (I also think that Romney/Alexander would be a stronger ticket than Romney/Thompson.) If Fred Thompson becomes president, I won't be surprised if Lamar Alexander ends up back in the cabinet at some level.
The headline of this blurb overplays the importance of this change. I don't know how Tennessee apportions delegates, but if Fred Thompson runs, no one else is going to get more than a few delegates from Tennessee. The fact that Marsha Blackburn originally supported Mitt Romney means that those who still don't trust Mr. Thompson because of things he did in the Senate may be influenced towards Mr. Romney because of her previous support. In terms of counting delegates for the nomination, this move means nothing.
Bill
ROFL!! You Romney guys crack me up. That's the funniest line I've read in a while.