Democratic Arkansas Senator Blanche Lincoln neither won nor lost Tuesday's primary battle against Lt. Governor Bill Halter, who ran to Lincoln's left, and D. C. Morrison, who ran to her right. Lincoln now faces a runoff election against Halter, scheduled for June 8. A moderate Democrat, Lincoln split with her party during key votes on health care reform but has been highly involved in pushing for financial regulatory reform. Here's why she's facing a runoff, what it means, and what's next for this race.

• White House vs. Organized Labor The Washington Post's Dan Balz and Chris Cillizza call this race "in many ways a proxy war between organized labor and the White House. Obama endorsed Lincoln and appeared in ads for her. But unions spent millions on television and radio ads -- not to mention an extensive field program -- to oust the incumbent, whom they believe has been insufficiently loyal on issues such as health care and the Employee Free Choice Act."

• Why Halter Did So Well   Politico's David Catanese observes, Halter's near-tie "is a win for groups like the Service Employees International Union (SEIU) and MoveOn.org that poured millions of dollars and thousands of hours into his insurgent bid and represents another striking rejection of incumbency. ... Halter's campaign initially grew out of anger about Lincoln's opposition to so-called 'card check' legislation that would make it easier for unions to organize and her strong aversion to the public option during the health care debate. But as the campaign progressed, the former Social Security administrator took a more populist tact, turning the campaign into a referendum on Lincoln's time in Washington and her ties to special interests."

• 'Remarkable' That She Didn't Lose  Slate's John Dickerson writes, "Blance Lincoln held on to win, which was a remarkable achievement given that she was considered finished a few months ago. But it may be only a temporary reprieve. Labor unions are going to continue working against her. They've had a very good night, securing the victory in Pennsylvania's 12th district and nearly defeating a powerful incumbent in Arkansas."

• Runoff Will Be About Attracting Conservatives   The Washington Post's Peter Slevin explains, "As the two Democrats pivot toward a runoff sure to be as intense as the race so far, they will be searching for ways to attract the 42,000 voters who cast ballots for Morrison, a conservative Little Rock businessman whose policy prescriptions include sealing the Mexican border and passing a national sales tax."

• Why It Probably Doesn't Matter  National Journal's Charlie Cook predicts a Republican win either way. "Lincoln is getting hammered by Democrats for not being sufficiently liberal or supportive of labor. The victor of a runoff is anyone's guess. But odds of this seat staying Democratic are very slim."

• Could This Affect Financial Reform?  Talking Points Memo's Brian Beutler writes, "A runoff election in Arkansas means Sen. Blanche Lincoln (D-AR), who didn't prevail in her primary Tuesday, stands to suffer if Democrats weaken her section of the bill, which would impose strict regulations on derivative trading, and, most controversially, would require financial institutions to spin their derivatives trading desks off into separate entities."

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