National Republicans are bringing pressure to bear on Sen. Larry Craig to resign his seat. The speed with which individual senators have reacted is stunning. A number of senators have even suggested that the Senate Ethics Committee launch its own investigation of Craig’s conduct. Why are Republicans moving so quickly?

First, the senator already pleaded guilty and that plea, freely entered into, is unlikely to be vacated. If it somehow is, how anxious are Republicans to have details of the incident replayed nightly in a highly publicized trial?

Second, the “culture of corruption” is fresh in the minds of the GOP, which suffered major losses of members tarnished by scandal in 2006. Given the major headwinds the party will face in 2008 on other matters, the last thing party leaders want is to have to face this issue again.

Third, Craig blindsided his fellow senators. He did not tell them about this incident, which occurred nearly two months ago. That is unforgivable and has earned him no goodwill among his fellow senators.

There is evidence that grassroots conservatives are reacting skeptically to the senator’s story. Right now, it seems less a question of whether Craig will resign, but rather, when.