Washington (CNN) -- Presumptive GOP presidential nominee Mitt Romney picked up more ammo in his quest for the White House, sweeping primaries in Montana, New Jersey, New Mexico, South Dakota and California on Tuesday night.
Though he had already won enough delegates -- 1,144 -- to clinch the Republican presidential nomination by last week, Romney technically remains the presumptive nominee until the party's convention in August.
While the big political story of the night was Wisconsin Gov. Scott Walker's victory of a recall vote, Congressional candidates duked it out in New Jersey, New Mexico and California, where redistricting forced some incumbents to battle one another.
Voters in California accustomed to casting ballots in party primaries saw something very different on Tuesday: All candidates, regardless of affiliation, competed in the same preliminary contest, with the top two finishers moving on to compete in the general election.
California's so-called "top two primary" was intended to stem political gridlock caused by elected officials at their parties' extremes. Similar measures are in place in Louisiana and Washington, but as the country's most populous state, California's ballot shakeup could mean big changes to state and national politics.
Two Congressional races in California pitted incumbents against each other, though the state's new system would make it possible for all to advance to November's general election.
Redistricting following the 2010 Census led to a match-up between Democratic Reps. Janice Hahn and Laura Richardson in the state's 44th Congressional District outside Los Angeles. In the San Fernando Valley, Democratic Reps. Brad Sherman and Howard Berman faced off in the 30th Congressional District.
With 100% of precincts fully or partially reporting by Wednesday morning, Hahn had 59.8% of the votes compared with Richardson's 49.2%.
Meanwhile, Sherman led his race with 42.2% of the votes, compared with Berman's 32.2%, with more than 81% of the precincts reporting.
Sherman and Berman are both long-serving members of the House -- Sherman has been in office for eight terms, while Berman is completing his 15th term on Capitol Hill. Both were re-elected in 2010 with large majorities, and both serve on the House Foreign Affairs Committee.
Given each man's longevity in office, it's possible they will both garner enough votes in Tuesday's primary to move on to the general election.
California voters approved "top two" primaries in a ballot initiative in 2010, a year after the state's legislature passed a measure instituting the new practice. Then-Gov. Arnold Schwarzenegger backed the nonpartisan primary measure, joining an effort that also included Willie Brown, the Democratic former mayor of San Francisco.
California held "blanket primaries" in 1998 and 2000, in which all registered voters could cast ballots, regardless of party affiliation. The United States Supreme Court struck down the practice, saying it violated political parties' First Amendment right of association.
New Jersey Rep. Steve Rothman conceded to Rep. Bill Pascrell after an incumbent vs. incumbent fight in the state's Democratic primary.
"Congratulations to Congressman Bill Pascrell and his team, wish them the best. Time to unite as Dems and re-elect President Obama," Rothman tweeted Tuesday night.
The race, however, was largely known for turning into a battle of campaign surrogates: former President Bill Clinton endorsed Pascrell, while President Barack Obama showed tacit support for Rothman.
Rothman and Pascrell are both eight-term congressmen who won re-election in 2010 with more than 60% of the vote.
The two men were angling for the same northern New Jersey seat this year after redrawn congressional lines placed Rothman's hometown into a conservative district.
Instead of challenging Republican Rep. Scott Garrett, Rothman moved to Englewood, where he once served as mayor, to run against Pascrell.
Obama, whom Rothman backed in 2008, met with the candidate at the White House on Friday. Photos showed the two politicians walking along the White House colonnade, though their meeting was private.
In a press release, Rothman's campaign said Obama "affirmed his support" for the candidate at the get-together, characterizing the move as a show of appreciation for Rothman's backing in 2008.
But Josh Earnest, the White House deputy press secretary, was careful Friday not to label the meeting as a show of endorsement.
"It means that the president has a longstanding relationship with Congressman Rothman, is appreciative of the solid working relationship that they've enjoyed while the president has been in office. It's indicative of the priorities that they share," Earnest told reporters aboard Air Force One.
Pascrell, a Hillary Clinton supporter in 2008, appeared alongside Bill Clinton at a campaign rally in Paterson on Friday. Clinton told supporters he was offering his endorsement because of his success working with Pascrell in the past, including during his time as president.
Both Pascrell and Rothman were elected in 1996, the same year Clinton was elected to a second term in the White House.
The two men have similar, left-of-center voting records in Congress. During the campaign, Rothman attempted to paint himself as the more progressive candidate, while Pascrell stumped as a pragmatic moderate.
In a Democratic U.S. Senate primary, voters in New Mexico chose Rep. Martin Heinrich over the state's auditor, Hector Balderas.
The two were competing to fill the seat occupied by Sen. Jeff Bingaman, a Democrat who announced in February he wouldn't run for another term.
The battle between Heinrich and Balderas was largely devoid of any major policy disagreements or personal attacks. In a debate Sunday, the two candidates went after the presumptive Republican primary winner, former U.S. Rep. Heather Wilson.
The Albuquerque Journal reported the only major disagreement during the debate centered on corporate tax rates, with Heinrich saying he supported lower tax rates on companies in order to lure them to do business in New Mexico.
"I think we need to have a lower, flatter, across-the-board corporate tax rate that actually brings more revenue into the federal government so that we can balance our budget and give a better deal to small companies here in New Mexico," Heinrich said, according to the newspaper.
Balderas said in the debate he supported lower tax rates for public employees, including teachers and firefighters.
CNN's Justin Lear and Holly Yan contributed to this report.