A round-up of this morning's must-read stories.

CLINTON OR OBAMA? MISSISSIPPI'S TIME.
(Natalie Chandler and Leah Rupp, Clarion-Ledger [Miss.])
Mississippi does not require voters to declare party affiliation when they register to vote. Therefore, residents who usually vote Republican can cast a ballot today for Obama or Clinton. But those voters would have to forgo voting in the Republican congressional primaries. Marty Wiseman, director of the Stennis Institute of Government at Mississippi State University, said he doesn't expect much crossover voting. It would take an organized effort by Republicans and a lot of money, he said. ... A few people approached state GOP Chairman Jim Herring at church, asking whether they should vote in the Democratic primary to skew the ballots toward one candidate or another. "We shouldn't be fooling in (the Democrats') business ... because we've got enough to deal with," said Herring, adding that crossover voting also would hinder a two-party system that political leaders have tried to foster.

MORE: Obama Hopes for Win in Mississippi (Sun-Herald)
Mississippi Democrats' Enthusiams High (Clarion-Ledger)
Obama: 'We Are at a Defining Moment' (Clarion-Ledger)

INFIGHTING WORRIES DEMOCRATS
(Jonathan Kaufman, Wall Street Journal)
The groups that for months have energized the Democratic campaign and have given Democrats high hopes -- blacks, women and young voters -- are increasingly sniping at each other, raising concerns that the battle could create problems in the November election... About 75% of Republicans say they are satisfied with Sen. McCain, compared with 24% who say they are dissatisfied... Among Democrats, 71% said they would be satisfied if Sen. Clinton becomes the nominee, while 28% said they would be dissatisfied; roughly the same number, 70%, would be satisfied with Sen. Obama; 29% dissatisfied. Although Sen. McCain is benefiting from having clinched the nomination, there is a marked change from January, when 81% of the Democrats said they were satisfied with their candidates, compared with 57% of Republicans who said they were happy with their field.

OBAMA REJECTS IDEA OF A BACK SEAT ON TICKET
(Jeff Zeleny and Julie Bosman, New York Times)
The Clintons’ decision to repeatedly invoke the idea of a Clinton-Obama ticket could serve several goals: to diminish Mr. Obama, of Illinois, in a genteel way, while courting some of his supporters by suggesting that a vote for Mrs. Clinton could ultimately be a vote for him, too. But as the specter of such a ticket has gained currency with the Clintons’ musings, Mr. Obama felt compelled Monday to try to stop the chatter by offering his most expansive answer yet on the issue. With a steady smile, his tone ranged from amused to mocking to derisive.

MCCAIN'S NEXT BIG TEST: ECON 101
(Jonathan Martin, Politico)
When the February jobs report came out on Friday, economists grimaced and Wall Street blanched. John McCain, however, said the news was “not terrible” — and Democrats pounced.  “Once again, John McCain demonstrated just how little he understands about the economy,” the Democratic National Committee declared in an e-mail to reporters.  McCain suffered in the Democratic translation of his remarks at a campaign stop in Georgia, as he had acknowledged the jobs news was “not good” and was not terrible only because the overall unemployment rate didn’t rise.  But the broadside was yet another example of what is already among the most popular lines of Democratic attack against McCain: that the Arizona senator lacks expertise on the economy and will be uniquely vulnerable on what is shaping up to be the overarching domestic issue of the campaign. 

MCCAIN PLANS TRIO OF TOURS FOR VOTERS TO REEXAMINE HIM
(Associated Press)
While Obama and Clinton fight on, McCain hopes to shore up his campaign financing, public image and political posture. Wednesday, McCain will hold his first general-election town hall meeting in a nostalgic locale: New Hampshire. The Exeter event is a nod to the state's role as host to the first primary McCain won en route to the nomination. In coming weeks, McCain also hopes to deepen voters' understanding of his background and policy views. His first effort comes in foreign policy next week. McCain will keep a previously scheduled commitment to join a congressional visit to European and Middle Eastern capitals. He plans to meet with a series of world leaders. Upon his return, McCain plans a major foreign policy address. Then McCain will take off on a biographical tour that will highlight his military service.

MORE: McCain's Health is 'Fine' (Los Angeles Times) 

THE VEEPSTAKES: THERE'S AN OBVIOUS WINNER
(Fred Barnes, Weekly Standard)
 McCain thinks three vice presidential picks from the recent past were wise: Republican Dick Cheney in 2000 and Democrats Joe Lieberman in 2000 and Al Gore in 1992. They were nationally known political heavyweights who passed the most important test. They were accepted almost instantly as ready to replace the president if necessary. And they had no significant drawbacks... That leads to Romney. He has run a vigorous national campaign and been vetted by the press and his opponents for the Republican nomination. These are very strong pluses. A pick who produces unhelpful surprises, as Geraldine Ferraro did in 1984 (her husband's business deals) and Dan Quayle did in 1988 (his National Guard duty), is exactly what McCain doesn't need. Romney is a known quantity.

MORE: Scanning for a GOP Running Mate (Gerald Seib, Wall Street Journal)