4) Maryland Gov. Martin O'Malley is wading into the 6th District Democratic primary on behalf of state Sen. Rob Garagiola in his tougher than expected race against John Delaney. O'Malley's endorsement puts him opposite Bill Clinton and Rep. Donna Edwards, who are backing Delaney. 3) On the campaign trail, you'll find a more restrained Rick Santorum. 2) Sheldon Adelson, the billionaire who has been the main source of money for a pro-Newt Gingrich super PAC has lost faith in the former speaker's candidacy, saying that Gingrich is "at the end of his line" in the race. 1) Sen. Marco Rubio, R-Fla., endorsed Mitt Romney on Wednesday. Rubio's nod is yet another sign of the increasing establishment support Romney is bringing together.. Rubio premised his endorsement out of his desire to end the Republican primary, fearing an elongated nomination fight would only help President Obama in the general election. He didn't sound at all excited about the candidate himself. He represented a large swath of conservative voters, who are likely to cast their ballots for Romney as a vote against Obama, not one for Romney. That said, Rubio is one of the few VP possibilities who could genuinely get the conservative grassroots excited about the GOP ticket. He's a compelling speaker who's one of the best articulator of conservative principles on the national stage. He hails from a must-win swing state. And his Hispanic background would give Romney a shot at making inroads within the Latino community, not to mention adding appeal to suburban independents by picking the first Hispanic on a national presidential ticket. Josh Kraushaar contributed.