With a bevy of heavy hitters like Bill Clinton and Sarah Palin stumping for candidates across the country, today's primaries could provide an insight into the strength of political endorsements and the mood of the electorate going into the heated November elections.
The Senate race in Colorado has pitted former President Clinton against President Obama. In the Georgia gubernatorial race, the power of former Alaska Gov. Palin's endorsement will be tested as her "Mama Grizzly" Karen Handel faces off against the Republican establishment favored Nathan Deal.
2010 Election Maps: Follow the Senate, House and Governors' Races
Here is a look at some of the top races to watch for tonight.
Colorado: Clinton vs. Obama
Nobody thought much of it back in late June when Clinton endorsed underdog Andrew Romanoff in Colorado. Michael Bennet, despite his never having run for office before, was appointed to the Senate seat there and he was the White House horse in the race, winning the backing of President Obama.
More on the 2010 Races in Colorado
Bennet had the lead and Clinton would not be stumping in person for Romanoff. But Romanoff's campaign of selling himself as a Washington outsider and not taking money from political action committees has propelled him in the race.
Armed with an endorsement from Clinton -- which also helped struggling incumbent Blanche Lincoln regain her ground in Arkansas -- Romanoff upped the rhetoric against Bennet, tying him to Wall Street and exploiting a New York Times expose about exotic and controversial loans taken out by the Denver Public School system when Bennet was superintendent.
Public polls show Bennet lost his initial lead over Romanoff and that the race is too close to predict, leading some to think that the president's endorsement may not carry as much weight as many initially had thought.
Hours before today's bellwether elections, Obama was nowhere near any of the states that are voting. Instead, he went to a fundraiser in Texas where he railed against former President George W. Bush.
"Obama's not even helping them run good campaigns by constantly attacking George W. Bush, looking backwards, not giving them any fodder to defend his policies," Republican strategist Mary Matalin said on "Good Morning America" today. "Of course, they're going to run away from him."
Some Democrats say the race is not about Obama's endorsement, but about how candidates are relating to voters.
"The president is gravy but what you need in every campaign is a lot of potatoes," Democratic strategist Donna Brazile said on "GMA." "They know that the president can provide the gravy, the sauce, but they really need to go out there and prove to voters that they're in touch with their values, that they are running to represent them in Washington."
While he won't appear in person in Colorado, the former president recorded an automated message that went out to some Colorado voters. Obama praised Bennet in a tele-town hall last week.
Pennsylvania: Both Parties Divided
Meanwhile, Clinton, ever popular with Democrats as a former president, will be out and about on the campaign trail. He will stump Tuesday in Pennsylvania for Rep. Joe Sestak, who defeated Sen. Arlen Specter, a former Republican, for the Democratic nomination.
There was mild controversy when it became clear earlier this year that the White House, through Clinton, had sought to dissuade Sestak from seeking the seat against Specter, its preferred candidate.
Democrats aren't the only ones with split endorsements on display Tuesday.
Georgia: Palin and Romney vs. NRA, Gingrich and Huckabee
There's an all-out endorsement war in Georgia -- Handel, the former secretary of state, has Palin and former Massachusetts Gov. Mitt Romney in her corner.
But Nathan Deal, the former Republican congressman, has some high-profile endorsements of his own -- the National Rifle Association, former House Speaker Newt Gingrich and Mike Huckabee.
In a fiery speech Monday, Palin blasted the "good-ole-boy" network that has accused Handel of being soft on abortion and of lacking a college degree. Handel in turn has accused Deal of corruption.
Republicans, however, have downplayed the endorsement wars in what has become an ugly fight over the state's gubernatorial seat.
"She's not taking on Newt Gingrich," Matalin said. "She's an outlet for the frustration and anger of people who have not just been dismissed, but disdained. She's an advocate for common sense conservatism."
"She is the story of this cycle," Matalin added.
Connecticut: From Wrestling Ring to Political Ring
Rep. Rob Simmons was supposed to be out of the Republican primary for senator in Connecticut. He shuttered his operation and went dormant more than a month ago.
But then, late in July, like Hulk Hogan getting up off the mat and doing that, "Can you hear me now" thing, Simmons re-emerged. He brought his campaign back to life (sort of) in the final stretch of the primary, hoping to knock off his professional wrestling entrepreneur rival. It's unlikely Simmons will prevail but interesting nonetheless.
Linda McMahon, the Republican frontrunner, is a successful businesswoman and has been running on her business acumen. But she has taken a beating in Connecticut for what that business is: professional wrestling.
Recent weeks have seen women's groups condemn some odd clips of McMahon and her husband doing their day job at WWE in recent years; talking smack, getting smacked by her daughter. Connecticut Democrats have compiled the most interesting videos here.
Back in Colorado, on the Republican side of the Senate race is Ken Buck, the Tea Party-favored Republican who stands a good chance of winning the nomination from Jan Norton, the former lieutenant governor.
Buck has the nod of strict conservative Sen. Jim DeMint and Norton has gotten praise but no endorsement from Palin. Norton has campaigned with Sen. John McCain, the 2008 Republican nominee.
He said some unfortunate things about his choice of footwear and remarked that people should vote for him because "I do not wear high heels." Buck is a gaffe-prone, sound-byte machine. He will present a test for the Tea Party. Read more on the year of the Republican woman here.
In the Colorado governor's race, the real tests will come in November. Former Republican Rep. Tom Tancredo, a firebrand in the anti-illegal immigration movement, has left his party to join the small-time American Constitution Party.
Should he stay in the race, his presence could give aid to Democrats, especially with the deeply flawed Republican candidate Scott McInnis, who has been accused of plagiarism.
ABC News' David Wright contributed to this report.