Ezra Klein's Wonkbook cites The Hill's report that Senate liberals are threatening not to vote for an energy bill -- especially one that promotes offshore drilling -- if it doesn't put a price on carbon. Sens. Frank Lautenberg, Sheldon Whitehouse, and Jeanne Shaheen have all made intimations to that effect.

Mike Allen's Playbook points to a Politico play-by-play of Rep. Joe Barton's apology for his apology to BP yesterday. Reps. John Boehner and Eric Cantor supposedly met with Barton when his energy and commerce subcommittee went on break, telling him that he would either apologize or lose his committee post.

Chris Cillizza's Morning Fix announces that the "spring training portion" of the 2012 presidential race has begun, with would-be candidates offering strategic endorsements in the hopes of attracting donations and support in key states. Today, Minnesota Governor Tim Pawlenty will back Ohio Rep. John Kasich's bid for governor and, also in Ohio, Jim Renacci's run for Congress.

The Daily Beast's Cheat Sheet notes ABC's report that Secretary of State Hillary Clinton revealed in an Ecuadorean interview that the U.S. is planning to sue over the Arizona immigration law.

ABC's The Note links to a Washington Post story about President Obama's lead-in to next week's G-20 meeting in Toronto. Obama sent a careful, at times sharply worded letter to world leaders seeking renewed cooperation on divisive global issues.