As New Jersey Democrats head to the polls Tuesday, Newark, N.J. Mayor Cory Booker remains the solid frontrunner in the primary contest for the Garden State's special Senate election.
Booker has always had a strong lead in the primary contest, but he nevertheless found himself opponents who criticized him from the left. In the deep blue state of New Jersey -- where a Republican hasn't been elected to the Senate in over 40 years -- the Democratic primary could be just as consequential as the general election. A Quinnipiac poll released last week showed that even with three Democrats running against him, Booker held a 37-point lead over his nearest primary competitor. In a head-to-head match-up against his likely Republican competitor Steve Lonegan, Booker has a 25-point lead among registered voters.
The winner of the general election -- a special election taking place in October -- will replace Sen. Jeff Chiesa, R-N.J., who was appointed to the seat in June after the death of Sen. Frank Lautenberg, D-N.J.
While Tuesday's New Jersey primary may not be that competitive, it kicks off a 2014 primary season that could generate some heat. Here's a look at some of the Senate primaries worth watching:
Incumbent senators have huge advantages -- Senate Minority Leader Mitch McConnell, R-Ky., for instance, has the name recognition of a congressional leader who's served in the Senate for nearly 30 years, not to mention close to $10 million in the bank to support his re-election.
Yet in the conservative state of Kentucky, longtime service and leadership in the Senate may be more of a liability than an asset. McConnell is facing one of the most serious primary challenges of the 2014 season from tea party-aligned businessman Matt Bevin, who is attacking McConnell for congressional dealmaking.
McConnell's campaign has aggressively fought back, nicknaming the tea partier "Bailout Bevin," referencing the federal bailout money he took for his companies in Connecticut. The senator's campaign wasn't helped, however, when McConnell's own campaign manager wastelling a fellow conservative, "I'm holding my nose" while working for McConnell.
If he can overcome the challenge from the right, McConnell will face Kentucky's Democratic secretary of state, Alison Lundergan Grimes, in the general election.
Sen. Mike Enzi, R-Wyo., is another longtime senator who finds himself in a high-profile primary. Last month, former Vice President Dick Cheney's daughteras he seeks a fourth term.
"Instead of cutting deals with the president's liberal allies, we should be opposing them, every step of the way," Cheney said when she announced her intentions.
The winner of the primary will likely win the general election in the conservative state, but many in the GOP have nevertheless called the primary challenge. Cheney's entry into the race will cause the "destruction of the Republican Party of Wyoming," former Sen. Alan Simpson, R-Wyo., said. "It's a disaster -- a divisive, ugly situation -- and all it does is open the door for the Democrats for 20 years."
The race comes at an interestingfor Republicans, split whether a solidly conservative record like Enzi's is enough to merit re-election, or whether conservatives should follow the more aggressive mold of Sen. Ted Cruz, R-Texas.
While Cheney argues she'd be the more authentic conservative, Enzi can argue he's a better representative of Wyoming -- Cheney only moved to the state last year.
"People expect you to earn it. They won't give it to you," Enzi told the Jackson Hole News&Guide. "That doesn't mean just talking to a few folks. That means getting a background in Wyoming so you can do what needs to be done."