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.
Here is a look at some of the top races to watch for tonight.
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.
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.
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.