Paul Mirengoff has an interesting assessment of why the Tommy Thompson campaign failed. It’s certainly true that Thompson (a) had real, valuable and creative governing experience but was (b) charismatically challenged to the point of near-paralysis.
But there were two other factors in Thompson’s demise as well: First, being a governor isn’t as important as it used to be in American politics because of the focus on national security issues since 9/11. Thompson had no foreign policy experience, an affliction that may eventually hurt Mitt Romney as well, especially if Republicans find that they actually can tolerate Rudy Giuliani (who doesn’t have much foreign policy experience, either, but makes a big thing about being tough on evildoers).
The other factor is that Thompson, much as he tried to pretend otherwise, simply wasn’t as conservative as the Republican base. Unlike Ronald Reagan and George W. Bush (and now Mitt Romney), who act as if Washington, D.C. were the capital of France, Thompson actually believes in government and practiced his beliefs in a creative, humane but highly efficient way, especially when it came to welfare reform in the early 1990s. That seems a terrible liability for a GOP candidate these days.