Good Monday morning. Senator Ted Kennedy will undergo surgery at Duke University this morning, followed by radiation treatment at a major Boston hospital, per a statement from his office. Allies on both sides of the aisle are rooting for him. Here's what else Washington is watching this morning:

-- The Senate is back in session this afternoon to take up a bill from Connecticut Independent Joe Lieberman and Virginia Republican John Warner on climate change. Despite his attention to the issue on the campaign trail, John McCain -- who spent the weekend in Washington, including an off-camera visit to Walter Reed Hospital -- won't be in the Senate to vote on the measure today. President Bush awards a medal of honor today before meeting with economic advisers, while Vice President Cheney presents a journalism award at the National Press Club.

-- Hillary Clinton scored a big win in last night's Puerto Rico primary, winning 68% to Barack Obama's 32% and a majority of the island's 55 delegates to the national convention. But per the latest delegate counts, Obama remains just 50 votes shy of an outright win. Clinton still has just over 200 delegates to go to reach the magic number of 2,118. Add up the number of delegates available in tomorrow's contests, in South Dakota and Montana, as well as the unallocated Puerto Rican delegates and supers yet to be chosen and Clinton would need to win approximately 85% of those remaining uncommitted to take the nomination. Obama, by contrast, needs just 20%.

-- But Clinton has relied on the popular vote argument in recent weeks, and she's up with a new advertisement in South Dakota and Montana touting the fact that no other candidate has ever gotten so many votes in a presidential contest. The latest RCP Popular Vote Count shows Clinton leading Obama by 303,000, when Michigan is taken into consideration, or by 65,000 when undeclared voters in the state are awarded to the Illinois senator. True, the popular vote doesn't count for much in a contest in which delegates matter, but it's the only argument Clinton has left, and it's compelling as well. If her campaign is serious about continuing, how long until the new advertisement hits national cable?

-- This weekend's Rules and Bylaws Committee meeting, full coverage of which you can find on Politics Nation, advanced Clinton's cause by leaps and bounds over the way the primaries have been going recently; it's not often that Clinton has been able to say she netted 24 delegates in a single day. But her two top backers on the panel, Harold Ickes and Tina Flournoy, remained apoplectic that Michigan delegates will not be seated in accordance with the results of the primary. The vote to reinstate Michigan and give Clinton a five-vote advantage, floated as a compromise, passed by a 19-8 margin, one vote more than the two-thirds required to carry. Ickes and Flournoy, two party power players, maintained their right to take the matter all the way to the convention's credentials committee.

-- Then again, the contest may not last much past tomorrow's final two primaries. The Clinton campaign will head to New York tomorrow night, though there will be fewer of them than there once were. Politico's Ben Smith and Amie Parnes report the campaign is getting rid of their remaining field staff, either an indication that the tent is about to fold or a recognition that, with the primaries over and the nomination slipping away, advance staff just aren't needed anymore and it's time to trim overhead. Clinton is weighing her options, the New York Times' Adam Nagourney writes, though the possibility that she heads to a convention is possible.

-- Obama, meanwhile, has not only begun campaigning in general election states, he's doing his best to begin the healing process. While some Clinton-backing protesters at this weekend's Rules and Bylaws Committee made it known they wouldn't vote for Obama in the Fall, the candidate is already playing nice with Clinton in hopes of getting her backing. Obama called Clinton from a stop near the Corn Palace in Mitchell, South Dakota yesterday to congratulate her on her win. Later, he praised her as "a great asset when we go into November to make sure that we defeat the Republicans, that I can promise you," per NBC/NJ's Athena Jones. The unity tour Clinton and Obama will eventually mount could prove one of the most critical periods of the entire contest.

-- That tour could begin shortly after polls close on Tuesday. Obama, expected to win both Montana and South Dakota, will rally at the Xcel Center in St. Paul, the site this September of the Republican National Committee. It's a gutsy move, inviting comparisons to what will be McCain's day in the sun. The campaign expects 20,000 people for the rally, approximately on par with the number of people who will hear McCain give his acceptance speech (GOP conventions, with approximately half the delegates Democrats have, are always attended by fewer people). Estimating liberally, if Obama wins 20 of the 31 delegates available tomorrow, he will still be 30 votes short of a clear majority. Today is the day he needs to roll out a heaping helping of super delegates. And it may be: By press time, he has already scored new super delegates from Virginia, California and Connecticut.

-- Mounting Problem Of The Day: Watch out for this, Republicans: There's a reason John McCain is only called your "presumptive" nominee and not the actual nominee. Remember that all the delegates to St. Paul have yet to be elected, and that smart politics can still influence who gets to go to Minnesota. In that state, along with Missouri, Washington, Nevada and others, the next round of the delegate selection process is inviting more Ron Paul supporters than anyone thought, as Jonathan Martin points out. As McCain gives his acceptance speech, the hundred or more Paul delegates could cause a massive headache with bells, whistles and any other noisemakers they can find, making for entertaining, but ultimately politically poisonous, television.

-- Today On The Trail: McCain delivers a keynote address to AIPAC, a pro-Israel organization, this morning in Washington before heading to Nashville, Tennessee, to host a town hall meeting. Obama has a town hall meeting of his own planned for Troy, Michigan, while wife Michelle stumps at get-out-the-vote rallies in Montana. Clinton is flying from Puerto Rico to South Dakota, where she has events scheduled for Rapid City, Yankton and Sioux Falls (RCP's Kyle Trygstad points out that in Yankton, Clinton will head down Tom Brokaw Boulevard, named for the local high school's most famous alum). Husband Bill is also holding events in the state today.