One story that you might not have come across, though, is that of Louisiana Senator David Vitter, implicated in the "DC Madam" story, and who has publicly admitted to having an extra-marital affair with a prostitute - having had his telephone number recorded as having been used for phone calls to the prostitute during roll call votes in the House of Representatives. The case is perhaps even more ironic when you consider that Vitter first became a Congressman when his predecessor resigned after a sex scandal.
Yet Republican Senators have lined up in support of Senator Vitter - the same Senators who were either silent or vocal in calling for Craig's resignation when that story broke. (There's another interesting parallel between the two cases, in that both Senators were important figures in Presidential campaigns - Craig for Mitt Romney; Vitter for Giuliani. Craig has been dropped from the campaign team, Vitter hasn't).
This has led some to suggest that it isn't a sex scandal that hangs a Republican out to dry. As long as you're having heterosexual sex, it's fine. Take this example from the Boston Globe:
Thus, the arrest of Craig, a forceful opponent of gay rights, for allegedly soliciting sex in a men's room stall, presented Republicans with a dilemma. The sordidness of Craig's alleged offense was deeply damaging to a party that had already suffered for having failed to expose the fact that former GOP lawmaker Mark Foley had sent lewd e-mails to male House pages.
However, the national party was still backing Senator David Vitter of Louisiana, who had acknowledged committing "serious sin" after his phone number allegedly appeared on a list provided by a Washington-area madam. Vitter's offense - which apparently involved a female prostitute - was less politically damaging than Craig's, based on home-state response.
Now, undoubtedly the irony of Craig's strong public stance against same-sex marriage contributed to the public interest in the story - and it was the prominent place it occupied in the news that contributed to the clamour for his resignation. While Vitter's conduct might not demonstrate the high morals expected of those in public office, it doesn't have so obvious a contradiction between public and private actions. (That said, phoning the DC Madam during roll call votes while on Capitol Hill does suggest a dereliction of public duty).
But there is a directly political explanation for the different reactions to the scandals, too. For Idaho is a solidly Republican state, with a Republican governor. And Craig's Senate seat is up for re-election in 2008. So when Craig resigns, the governor will appoint a temporary replacement - who will be a Republican, and thus maintain Republican numbers in the finely-balanced Senate (the Democrats have a 51-49 advantage, if you count the Independents who caucus with them; but in a system where the self-interest of the state can cause people to break ranks, it is barely enough to guarantee victory on any vote). And, more to the point, the new Senator, whoever he or she may be, will have the advantage of incumbency come 2008 - a significant advantage in a political system where name recognition seems to count for a lot. With a year's chance to get settled in, there is a good chance of making sure the shadow of Larry Craig does not loom over the next election.
Louisiana, on the other hand, has a Democrat Governor, Kathleen Blanco. Were Vitter to resign, she would appoint a Democrat to fill the vacancy until a special election was held in 2008 - thus ceding the incumbency advantage to the other party - and in a state where the outcome of a Senatorial election would be much in doubt. And that would be a waste of a valuable seat when there is no need to put it up for grabs until 2010 - by which point the scandal would be a distant memory. Even if it were to be brought up, there is another three years in which Vitter can bring up extra achievements to demonstrate his utility to the people of Louisiana.
It's very easy to be indignant about scandals when your party's political standing isn't on the line. Cut the dead wood adrift, and the Republicans can take a stand for morality whilst their power in the Senate remains the same. I think we might have seen more prepared to stand up in support of Larry Craig if he was Senator for a swing state. In Idaho, anyone can be a Senator if they're a Republican. In Louisiana, they can't. Larry Craig is an expendable friend; David Vitter isn't. That's why Craig went - regardless of the details of his sexual indiscretions.