Perhaps the most outspokenly liberal member of the speculative Democratic crop, Maryland Gov. O'Malley has been at the forefront of his state's fight over gay marriage, which was legalized via a ballot initiative. And his speech during the Democratic National Convention was a particularly left-leaning address. Plus, O'Malley has already passed the Iowa litmus test, visiting a steak fry event hosted by Sen. Tom Harkin.
Alex Wong/Getty Images