Missouri sources tell NRO that Bond’s retirement comes as a huge surprise. Before Christmas, he was interviewing people for his re-election campaign.

Another surprise is that former House Republican Whip Roy Blunt (R.) is indeed interested in the seat, having left the House leadership. Other possible candidates on the GOP side include former Rep. Kenny Hulshof (R.), whose run for governor last year did not go well, and Lt. Gov. Peter Kinder (R.), who folded his gubernatorial run and won re-election last year instead.

On the Democratic side, you have to like Secretary of State Robin Carnahan (D.), daughter of the late Mel Carnahan, who was famously elected to the state’s other Senate seat posthumously in 2000.