Good morning politicos, here’s the Buzz. The budget battle begins, and the first skirmish is between Gov. Corbett and the Senate GOP. And Santorum finally pulled the trigger.

Santorum Endorses Romney: In an email to supporters, former Sen. Rick Santorum made a much-anticipated announcement Monday night and endorsed Mitt Romney’s presidential candidacy.

A Tim Holden Post Mortem: Two weeks ago, Lackawanna County Attorney Matt Cartwright unseated Rep. Tim Holden, the dean of the Pa. congressional delegation. Details, reports and analyses after the fact shed some light on how an incumbent who’d dodged 20 years of challengers fell.

AFL-CIO Targets Romney in PA Online Buy: Labor is looking at the Keystone State to hold the line against Mitt Romney in 2012. PA will see a significant chunk of the $500K the AFL-CIO Super PAC Workers’ Voice is spending on its national online ad buy.

PAGOP Video: I’m Not #Julia: With the help of 6 Pa. women, the PA Republican Party is taking a swipe at the President Obama – and his campaign’s “Life of Julia” feature.

Murphy Joins GOP Calls for Re-Redistricted Raja Seat: Rep. Tim Murphy is joining the ranks of his fellow GOP members in asking the LRC to reconsider their newly adopted map. Murphy said the new map would disenfranchise voters, especially in the 37th district where Raja is seeking State Senate election.

First Obama Campaign Ad to Air in PA (Watch Video): The general election ad wars are officially on in Pennsylvania. Barack Obama’s campaign rolled out this 60-second spot, called “Go,” a broad summary of the President’s re-election argument.

Legislative Election Updates:

SD-15: Rob Teplitz is the Dem running for the seat of retiring Sen. Jeff Piccola (R-Dauphin). It’s among the top pickup targets for Dems this cycle. One problem: he doesn’t live in the newly drawn version of the district. The city of Harrisburg was moved to Mike Folmer’s seat to help shore up the GOP in SD-15. Teplitz testified at the LRC yesterday:

“On behalf of this community that I love, I urge the commission to put all other motivations aside and approve a map that will meet the standards of state law, common sense, and fairness; that will be in the best interest of the community; and that will respect the expectations of the over 37,000 voters who cast their primary ballots for a state Senator to represent the 15th district.”

HD-42: Rep. Matt Smith (D-Allegheny) is looking good for re-election. He managed to secure enough write-in votes to make the Republican ballot, too, his campaign said: 343.

HD-66: Chris Dush, the man who came within 500 votes of unseating Speaker Sam Smith (R-Jefferson), will not be on the ballot in the fall. No on earned enough write-in votes to win the Dem nomination.

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Editor’s note: This week is a transition time for PoliticsPA and our regular collection of news clips will be abridged.

Capitolwire: Senate GOP proposes $27.65 billion budget, restores almost all higher ed cuts