They would have gotten better results running O'Malley for this seat, instead of allowing him to launch a gubernatorial campaign.
Something tells me that Cardin's political skills have atrophied.
Running in an overwhelmingly liberal, overwhelmingly white Dem. bastion for the past two decades isn't the best preparation for a highly competitive primary and/or general election.
I find it remarkable that someone in consistent major elective office for 40 straight years (20 in the State House, 20 in the U.S. House) would jump into a Senate race to be a minority party backbencher as Cardin would be (contrasting 30 years ago when he was a powerful House Speaker). As is pointed out, he's never really had to wage a competitive race (I'm not sure even his '86 contest to succeed Babs Mikulski was competitive). He probably realizes this is his last hurrah to have an impact statewide (as he passed up a prime opportunity to run for Governor in '02).