ELECTION/PRIMARY DAY IN EIGHT STATES….For early-June, today is a surprisingly important day for elections nationwide. Voters in eight states will go to the polls, including what will probably be the most important race between now and November. Among the highlights:

California’s 50th congressional district: The race to pick Duke Cunningham’s replacement was supposed to be easy for the GOP. It’s a conservative San Diego district, which backed Bush over Kerry by double digits two years ago. Today, however, Francine Busby (D) will face former Rep. Brian Bilbray (R), and it’s too close to call. The Republican establishment, in a near panic over what a defeat here might mean nationwide, has spent about $5 million on the race, and sent as many as 150 operatives to the district to eke out what they hope will be a narrow victory. The winner will fill the seat immediately, but stand for re-election in the fall.

California’s Democratic gubernatorial primary: State Treasurer Phil Angelides and State Controller Steve Westly have fought a very nasty primary for the right to take on Gov. Arnold Schwarzenegger (R). The San Diego Union-Tribune reported today that the results may be unclear for up to a week due to absentee ballots and a “laborious” manual counting system.

Montana’s Democratic Senate primary: State Senate President Jon Tester will face state Auditor John Morrison today, the winner of which will take on Abramoff-plagued Sen. Conrad Burns (R). Tester seems to have the momentum, though polls show the two about even. The winner has a real shot at picking up the seat; a recent Mason-Dixon poll showed Burns trailing both of his Democratic rivals.

Alabama’s gubernatorial primaries: On the Republican side, incumbent Gov. Bob Riley is poised to crush theocrat Roy Moore in the GOP primary, while among Democrats, Lt. Gov. Lucy Baxley is expected to beat former Gov. Don Siegelman, who has been running despite facing racketeering and bribery charges.

Iowa’s Democratic gubernatorial primary: In the race to succeed Gov. Tom Vilsack (D), Democrats will choose between Iowa Secretary of State Chet Culver, former state economic development director Mike Blouin, and state Rep. Ed Fallon. The most recent Des Moines Register poll showed Culver with an eight-point lead over Blouin, his closest rival. The winner will take on Rep. Jim Nussle (R) in November.

New Jersey’s Senate primaries: Sen. Robert Menendez (D) and state Sen. Tom Kean Jr. (R) are supposed to cruise to easy victories, but keep an eye on the GOP primary. Conservative activist John Ginty (R) has picked up considerable far-right support, and if Kean doesn’t win by a lot, it could reflect trouble for him in November.

So, any predictions?

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.