The successful Presidents, both Roosevelts, Reagan, and several in the ninteenth century had all been Governors. The notable exception to this concept is, of course, Jimmy Carter. Although a Governor (GA) he seems to be the single most discreditable President we've ever had. I blame him for the advent of all this Islamic rage. Surely the world would have been a better place had he simply not run, or, better yet, lost.
Your case could be contested.
F.Roosevelt, the man who dragged out the Great Depression for nearly 10 years, a successful president?
T.Roosevelt a successful president but I doubt it was because he had a whopping 2 years as governor under his belt. He spent far more time as a legislator.
By this argument Clinton, a governor of 12 years, should be a whopping success with all that experience. He wasn’t. Bush Sr. was a better president. Look how he managed the complexities of the Gulf War and the coalition; slick could’ve never done that.
Andrew Johnson was not a modern president, so it’s hard to compare. It could be argued whether Truman was an effective president.
One more thought: while it is nice to have executive experience, it is also nice to have foriegn policy experience which governors rarely have.
Me, no, personally I think it has to do more with Senator’s voting records hurting them in the primaries. A legislator can only take credit for what he has written and voted for. Governors (and mayors) take credit for stuff they didn’t push a pencil for all the time. It’s easy to do that with all the stuff going on in a state. There’s nothing to arbitrarily take credit for from inside a senate office unless you’ve done it yourself.