Of everyone on the list, Gov. Martin O’Malley of Maryland is the most open about his intentions.
“By the end of this year, I think we’re on course to have a body of work that lays the framework of a candidacy for 2016,” Governor O’Malley told reporters in August 2013.
After two terms as governor, O’Malley leaves office in January 2015. But he is campaigning hard nevertheless - for other Democrats, notably in early presidential primary and caucus states (Iowa, New Hampshire, and South Carolina). He's also building connections to other key Democrats in those states.
Since taking office in January 2007, O’Malley has worked his way up the ranks of the Democratic Governors Association (DGA), serving as chairman in 2011 and 2012 – a position that allowed him to build connections, and goodwill, with Democrats around the country. He’s also a regular on national cable news.
In 2009, Governing magazine named O’Malley one of its “Public Officials of the Year.” The magazine cited his data-driven approach, both as governor and as a two-term mayor of Baltimore before that. He has signed legislation legalizing gay marriage and in-state college tuition for illegal immigrants in Maryland, and both measures were supported by Maryland voters on Election Day. But major problems with the state's health-care exchange, MarylandHealthConnection.gov, could ding O'Malley's image of competence.