Martin O'Malley's campaign crashed and burned for good reason in 2015/2016.  He's not as overtly criminal as Clinton, but the Teflon Leprechaun has plenty of baggage - Baltimore come to mind.  He's about as fiscally responsible as my 5 year old.  He's about as "middle of the road" as Tim Kaine or Mark Warner down the road in VA.  Their campaigns and voting records say 2 different things.   Same thing goes for the other also rans last election, like Jim Webb or Lincoln Chaffee.