Primary Primer: A Quick Guide to Key Races in Today's 8 State Elections

Eight states—including heavyweights such as California and Iowa—are holding primary elections today, with congressional and gubernatorial seats at stake.

Seven of these states (Alabama, Iowa, Mississippi, Montana, New Jersey, New Mexico, and South Dakota) are holding U.S. Senate primaries. Republicans need to win six seats total in the November elections to wrest control of the Senate from Democrats. 

Additionally, five states (Alabama, California, Iowa, New Mexico, and South Dakota) will vote on gubernatorial candidates today.

Here are some of the more anticipated races: 

Alabama  House race: Seven candidates are competing for the spot of retiring Republican Rep. Spencer Bachus in Alabama's heavily conservative 6th district, and a runoff looks likely. Among the GOP hopefuls are charter school advocate and orthopedic surgeon Chad Mathis; state representative and Judiciary Committee Chair Paul DeMarco; Tea Party–favored Sen. Scott Beason; Alabama Policy Institute founder Gary Palmer; and businessman Will Brooke, who took a handgun, rifles, and a wood-chipper to a copy of the Affordable Care Act during his campaign. The winner will face Democrat Avery Vise in November. 

California: Governor's race: Democratic Gov. Jerry Brown is seeking a fourth term this fall. Republicans competing to face off against him include anti-immigration, Tea Party–backed state Assemblyman Tim Donnelly, who sees himself as a "threat to the country-club Republicans," and Former Assistant Treasury Department Secretary Neel Kashkari, backed by Condoleezza Rice and former Florida Gov. Jeb Bush. 

House races: With Rep. Henry Waxman retiring after 40 years in Congress, a bevy of Democrats stepped up for a chance to replace him. Sixteen candidates now face off today in California's 33rd District, based in Los Angeles county. 

In the Silicon Valley area, seven-term incumbent Rep. Mike Honda (D-Calif.)—backed by President Obama and major liberal groups such as the AFL-CIO—could face an upset from former Obama administration official Ro Khanna, backed by the likes of Yahoo CEO Marissa Mayer, Google Chairman Eric Schmidt, and PayPal co-founder Peter Thiel. 

And in the 31st district, representing the Inland Empire, "the primary has caused a rare split in both the national Democratic establishment and among progressive women's groups," HuffPost Politics bloggers Amanda Terkel and Samantha Lachman write. Pro-choice PAC Emily's List backs attorney Eloise Gomez-Reyes, while the Democratic Congressional Campaign Committee and NARAL Pro-Choice America have endorsed Redlands Mayor Pete Aguilar. On the Republican side Paul Chabot, a retired navy officer, is favored to beat former congressional staffer Lesli Gooch here. 

Iowa Senate race: Five Republicans are vying for their party's nomination, with state Sen. Joni Ernst—who gained national attention talking about castrating pigs—going into Election Day as frontrunner. Ernst has garnered the support of both Tea Party types such as Marco Rubio and establishment Republicans such as Mitt Romney. But it's unclear whether Ernst has enough support to get 35 percent of the primary vote—if no candidate crosses this threshold, than voters essentially cede nominating power to the state party convention, which takes place later this month. Democrat Bruce Braley is running unopposed for his party's nomination. 

Mississippi Senate race: On the establishment Republican side, six-term Sen. Thad Cochran (the second-oldest Senate incumbent running for re-election this year) faces off against Tea Party–backed state Sen. Chris McDaniel, who's earned endorsements from Rick Perry and Sarah Palin. The two men were nearly tied in polls going into election day, but "a bizarre scandal" involving McDaniel supporters scheming to exploit Cochran's dementia-ridden wife may wind up hurting McDaniel's chances. 

Montana Senate race: Democratic Sen. John Walsh, appointed four months ago, is fighting against former Lt. Gov. John Bohlinger and rancher Dirk Adams in the Democratic primary. Three candidates—U.S. Rep. Steve Daines, state Rep. Champ Edmunds, and newcomer Susan Cundiff—are vying on the Republican side.

House race: Five GOP candidates are competing in the primary for the state's lone House seat. On the Democratic side, first-time candidate John Lewis competes against former Montana House speaker John Driscoll.

New Jersey House race: The retirement of GOP Rep. Jon Runyan has opened up an ugly battle between Tea Party–backed businessman Steve Lonegan and establishment-backed businessman Tom MacArthur. Both are former North Jersey mayors. 

New Mexico Governor's race: In New Mexico, several Democrats—including Attorney General Gary King, Santa Fe businessman Alan Webber, and state Sen. Howie Morales—are competing to take on current Republican Gov. Susana Martinez. 

South Dakota Senate race: Former Republican Gov. Mike Rounds is competing against four others for the Republican nomination. To win, a candidate must get at least 35 percent of the vote; otherwise a runoff between the top two candidates will be held August 12.