There won't be any nastiness in any potential primary debates, at any rate, I don't think. He's worked with both Clintons before.
http://www.washingtonpost.com/local/md-politics/bill-clinton-loves-martin-omalley-even-if-omalley-runs-against-hillary-rodham-cinton/2014/05/14/8143dd4c-db73-11e3-bda1-9b46b2066796_story.html
Bill Clinton loves Martin OMalley. Even if OMalley runs against Hillary Rodham Cinton.
OMalley has said that he is actively preparing for a potential 2016 presidential run and cannot afford to wait to hear whether Hillary Rodham Clinton who would be a heavy favorite is going to move forward with a bid. The two spoke by phone last year, according to OMalley aides, and Hillary Clinton gave OMalley her blessing to do what he needs to do to prepare.
Any awkwardness about the situation was not apparent on stage Tuesday night. In fact, the former president went out of his way to praise OMalleys leadership during his two terms in the Annapolis statehouse. ... As mayor of Baltimore, OMalley got to know both Clintons when he was part of the delegation on a presidential trip to Ireland in 2000.
OMalley and the former president also came into contact through the Democratic Leadership Council, a centrist policy organization. And after the Sept. 11, 2001, terrorist attacks, OMalley worked with then-Sen. Hillary Clinton on homeland security measures.
Bill Clinton cut a television ad for OMalley during his 2006 campaign for governor. And in early 2007 just a few months after being installed in Annapolis OMalley became the second governor in the country to endorse Hillary Clintons 2008 presidential bid.