While today marks the end — at long last — of the presidential primary season, Congressional primaries are just heating up. In fact, with voters in seven states going to the polls today, this is the busiest day for Congressional primaries until Sept. 9.

Although some races are uncontested, voters will be choosing nominees for six Senate seats and 83 House seats today — except in New Jersey’s 1st district, where a placeholder Democratic candidate is expected to win the primary, but party bosses will decide later who the nominee will actually be.

Three races have been particularly noteworthy — and nasty: the Democratic Senate primary in New Jersey, the Republican Senate primary in New Mexico and the Republican primary in California’s 4th district.

In New Jersey, Rep. Robert Andrews (D) turned most of the state’s powerful Democratic establishment against him by launching an 11th-hour challenge to 84-year-old Sen. Frank Lautenberg (D). The incumbent appears to have the edge, based on institutional support alone, but Andrews’ generational-based appeal is resonating in some quarters, and he recently snagged the endorsements of the Philadelphia Inquirer and Newark Star-Ledger.

In New Mexico, GOP Reps. Steve Pearce and Heather Wilson have been slugging it out for the right to replace iconic Sen. Pete Domenici (R), who is retiring after six terms. Wilson, the more moderate of the two, may have more statewide appeal in a general election, but Pearce appears to have the edge with conservative primary voters. The winner today will start the general election as the underdog to Rep. Tom Udall (D). The loser may well be the frontrunner for the GOP nomination in the 2010 gubernatorial election.

In California, state Sen. Tom McClintock, a hero to conservatives in the Golden State and nationwide, is bidding for the GOP House nomination against former Rep. Doug Ose, a moderate who held the adjoining 3rd district seat for six years. Based on his appeal to conservatives, McClintock should be the favorite, but Ose is a savvy politician who is well-known in the Sacramento region and has spent his own money freely. The Republican primary winner will face 2006 Democratic nominee Charlie Brown, who came within 3 points of ousting Doolittle.

Here is a look at what’s at stake today, from coast to coast.

ALABAMA

What’s on the ballot
Democratic Senate primary to determine who will challenge Sen. Jeff Sessions (R); primaries in seven House districts.

Top primaries

Senate
Likely Democratic Senate nominee: state Sen. Vivian Davis Figures
Race outlook: Safe Republican

2nd district
Open seat held by Rep. Terry Everett (R)
Leading Democratic candidate: Montgomery Mayor Bobby Bright
Leading Republican candidates: state Rep. Jay Love and state Sen. Harri Anne Smith
Race outlook: Leans Republican

5th district
Open seat held by Rep. Bud Cramer (D)
Leading Democratic candidate: state Sen. Parker Griffith
Leading Republican candidate: advertising executive Wayne Parker
Race outlook: Tossup

CALIFORNIA

What’s on the ballot
Primaries in 53 House districts

Top primaries

4th district
Open seat held by Rep. John Doolittle (R)
Leading Democratic candidate: 2006 nominee Charlie Brown
Leading Republican candidates: state Sen. Tom McClintock and former Rep. Doug Ose
Race outlook: Likely Republican

52nd district
Open seat held by Rep. Duncan Hunter (R)
Leading Democratic candidates: teacher Vickie Butcher and retired Navy officer Mike Lumpkin
Leading Republican candidate: Marine Reservist Duncan D. Hunter, the retiring Congressman’s son
Race outlook: Safe Republican

NEW JERSEY

What’s on the ballot
Senate primaries in both parties for seat held by Sen. Frank Lautenberg (D); primaries in 13 House districts.

Top primaries

Senate
Likely Democratic nominee: Lautenberg
Likely Republican nominee: Ex-Rep. Dick Zimmer
Race outlook: Safe Democratic

3rd district
Open seat held by Rep. Jim Saxton (R)
Likely Democratic nominee: state Sen. John Adler
Leading Republican candidates: Ocean County Freeholder Jack Kelly and Lockheed Martin Vice President Christopher Myers
Race outlook: Leans Democratic

7th district
Open seat held by Rep. Mike Ferguson (R)
Likely Democratic nominee: state Assemblywoman Linda Stender
Leading Republican candidates: state Sen. Leonard Lance and political activist Kate Whitman
Race outlook: Tossup

NEW MEXICO

What’s on the ballot
Senate primaries in both parties for the seat held by retiring Sen. Pete Domenici (R); primaries in three House districts.

Top primaries

Senate
Democratic nominee: Rep. Tom Udall
Leading Republican candidates: Reps. Steve Pearce and Heather Wilson
Race outlook: Leans Democratic

1st district
Open seat held by Wilson
Likely Democratic candidate: Albuquerque City Councilor Martin Heinrich
Likely Republican nominee: Bernalillo County Sheriff Darren White
Race outlook: Tossup

2nd district
Open seat held by Pearce
Leading Democratic candidates: Doña Ana County Commissioner Bill McCamley and former Lea County Commissioner Harry Teague
Leading Republican candidates: retired banker Aubrey Dunn Jr., Hobbs Mayor Monty Newman and restaurateur Ed Tinsley
Race outlook: Likely Republican

3rd district
Open seat held by Udall
Leading Democratic candidates: state Public Regulation Commission Chairman Ben Ray Lujan and housing developer Don Wiviott
Likely Republican nominee: former Domenici aide Marco Gonzales
Race outlook: Safe Democratic

IOWA

What’s on the ballot
Republican Senate primary to determine the nominee against Sen. Tom Harkin (D); five district primaries.

Top primaries

Senate
Likely Republican nominee: former state Rep. George Eichhorn
Race outlook: Safe Democratic

3rd district
Democratic primary featuring Rep. Leonard Boswell and former state Rep. Ed Fallon, who ran for governor in 2006
Republican nominee: ex-Congressional aide Kim Schmett
Race outlook: Safe Democratic

MONTANA

What’s on the ballot
Republican Senate primary to determine the nominee to challenge Sen. Max Baucus (D); Democratic House primary to determine the nominee to challenge Rep. Denny Rehberg (R).

Top primaries

Senate
Leading Republican candidates: Engineer Kirk Bushman and state Rep. Michael Lange
Race outlook: Safe Democratic

House
Likely Democratic nominee: retired Army National Guard Lt. Col. Jim Hunt
Race outlook: Safe Republican

SOUTH DAKOTA

What’s on the ballot
GOP primaries to find nominees to take on Sen. Tim Johnson (D) and Rep. Stephanie Herseth Sandlin (D).

Top primaries

Senate
Likely Republican nominee: state Rep. Joel Dykstra
Race outlook: Safe Democratic

House
Likely Republican nominee: Wealthy businessman Chris Lien, an executive in his family’s sand and gravel business
Race outlook: Safe Democratic