I agree with Mark Danziger that, if for no other reason, Craig should resign for this:

According to the police report, the senator presented a business card and asked, “What do you think about that?”

Of course, it’s just one step beyond what most, if not all Senators do for special privileges. John Kerry was famous for his “Do you know who I am?” incidents to take cuts in line, get into restaurants, etc., which were apparently legion in Massachusetts, and other places. Senators (and Congresspeople) being human, are going to abuse their power for privilege, but an attempt to intimidate a law officer goes over a line.

[Update a few minutes later]

While I think that he should resign, I also think that this would be a perfectly appropriate response from him should he be asked by the press:

…if I were a Senator asked to vote to expel him from office, my public answer would be,