I think Larry Hogan will be like Bill Weld in 2018, as long as it isn't like a 2006 environment. All the A list candidates, like Ruppersberger, Gansler, Franchot, and Leggett may well decide it isn't worth the risk running against a popular incumbent like Hogan and take a pass, and Hogan gets a B or C list challenger. I think O'Malley is more likely to let his presidential bid run his course and hope for Cardin to retire in 2018 so he can slide right into the Senate.
LOL Gansler and Franchot are F list candidates, two of the most personally unpleasant people you'll ever meet. No one knows Ruppersberger, anyways.