A Bit More on Fred Thompson
Just to add a little more meat to this conversation....
It's worth noting that Fred Thompson, whose wife lived with her boyfriend for most of a decade—though there's some debate about whether they were actually married—and who is himself divorced, voted for the Defense of Marriage Act, which would institute a federal ban on gay marriage. (So much for federalism.) He also voted against prohibiting job discrimination based on sexual orientation.
So, yes, I think his marriage to Jeri Thompson, as well as his own divorce, are fair game. When you start discriminating against people who want to get married—but you don't hesitate to marry and divorce yourself—and your new wife may or may not have been married, no one's really saying—then sure, Jeri Thompson is an issue.