The fate of one vulnerable incumbent -- along with the outcome of more than a dozen competitive primary contests -- will be decided by voters in 12 states today in an election that's being called the "Super Tuesday" of the 2010 political season.

When polls close today, the primary season will be at its midpoint, with 25 states having held official primaries and 25 states to go before the November. The general election will decide control of Congress and, possibly, the future of President Obama's agenda.

Recent elections in Pennsylvania, Kentucky and West Virginia and a convention in Utah have reinforced what polls have been predicting for months: Voters are worried about the economy, fed up with Washington and wary of incumbents, often regardless of party. Today will provide insight into whether those concerns continue.

On the busiest primary day of the year, here are some of the races to watch:

Arkansas: Sen. Blanche Lincoln faces Lt. Gov. Bill Halter in a competitive runoff for the Democratic Senate nomination after neither candidate cleared the 50% vote threshold in May. Lincoln, a centrist, has come under fire from labor unions upset over some of her votes this year on Obama's health care plan (she supported the underlying measure but opposed a government-run health plan). Polls close at 8:30 p.m. ET.

California: There are several races of note. For starters, two wealthy Republicans – former eBay CEO Meg Whitman and state insurance commissioner Steve Poizner -- are spending millions of their own money for the GOP nomination for governor. Whoever wins will likely take on the state's Democratic Attorney General (and former governor) Jerry Brown.

For Senate, former Hewlett Packard executive Carly Fiorina is battling with former Rep. Tom Campbell and Tea Party favorite Chuck DeVore to take on Democratic Sen. Barbara Boxer in November. Polls close at 11 p.m. ET.

South Carolina: Politics has gotten personal in the Palmetto State. State lawmaker Nikki Haley hopes to replace Mark Sanford as governor, but the race for the GOP nomination has turned tabloid with recent allegations of infidelity, which she denies. Polls have Haley ahead of Lt. Gov. Andre Bauer, Rep. Gresham Barrett and Attorney General Henry McMaster.

In South Carolina's 4th Congressional District, six-term Republican Rep. Bob Inglis faces a challenge from former federal prosecutor Trey Gowdy. Like many intra-party fights on the GOP side, this race has turned partly on the 2008 bank bailout, which Inglis supported. Another issue that's come up in the race: Inglis voted to censure fellow South Carolina Rep. Joe Wilson after he shouted "you lie" at Obama during an address to Congress. Polls close at 7 p.m. ET.

Nevada: The GOP Senate primary will determine who will take on Senate Majority Leader Harry Reid in November. Heading into the primary, Tea Party backed Sharron Angle appeared to have the lead against former party official Sue Lowden and businessman Danny Tarkanian. Polls close at 10 p.m. ET.

New Jersey: Former Philadelphia Eagle Jon Runyan is hoping to win the Republican nomination to take on Rep. John Adler, a Democrat elected in 2009 in a southern New Jersey district that tilts Republican. Polls close at 8 p.m. ET

Georgia, Iowa, Maine, Montana, North Dakota, South Dakota and Virginia and are also holding primaries (Georgia's race is a special runoff for a vacant House seat).

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