Chris Christie, a former U.S. Attorney, won Tuesday’s Republican primary for governor of New Jersey, earning the nomination to challenge incumbent Gov. Jon Corzine in what is expected to be a competitive race this fall.

Christie — who was declared the winner by the Associated Press a little more than two hours after the polls closed at 8 p.m. eastern — lived up to his status as the consensus front-runner in the GOP contest, while Corzine easily defeated three lesser-known contenders in Tuesday’s Democratic primary.

With nearly all precincts reporting, Christie held a 55 percent to 42 percent lead over Steve Lonegan, the former mayor of the New York City suburb of Bogota, who tried during the campaign to persuade the Republican primary voting base that he was the more conservative candidate.

“The message unfortunately was not clear enough, and I take responsibility for that,” Lonegan said in his concession speech Tuesday night, according to the Associated Press. “The voters have spoken.”

The third Republican in the race, state Assemblyman Richard Merkt, had 3 percent.

Polls suggest that Christie may be a formidable threat to Corzine’s re-election hopes. The incumbent has endured low approval ratings in surveys of New Jersey residents, which some pollsters say is related to the state’s flagging economy as well as criticisms launched directly at Corzine for a failure to overhaul the state’s property tax system and Corzine’s proposal to raise tolls on the state’s highways to address New Jersey’s fiscal problems. Christie ran on a platform of lower taxes and reduced government spending, and touted his record as a prosecutor.

Christie’s status as the favorite in the Republican contest was symbolized both by the fact that the state Republican Party establishment rallied around his candidacy, and the fact that groups associated with the Democratic Party did not wait until after the primary to launch attack ads against him.

A political organization funded in part by the Democratic Governors Association ran a television ad during the primary campaign that attacked Christie’s record as a prosecutor. The commercial accused Christie of running pay-to-play schemes with government contractors.

The Republicans, though, also began an assault on Corzine’s record as governor long before the primary vote, which was echoed Tuesday night by Republican National Committee Chairman Michael Steele in a statement congratulating Christie on his victory. Steele said, “ Jon Corzine ’s ineffectiveness and failed policies have saddled New Jersey taxpayers with the heaviest tax burden in the country and driven jobs from the state. Chris offers New Jersey Republicans and Democrats alike the chance to break with Jon Corzine ’s failed Wall Street policies and once again make New Jersey’s cities and small towns engines for economic growth.”

The Republican Governors Association also launched a Web site during the primary campaign to criticize Corzine’s tax proposals and link to their paid advertising.

Christie consistently positioned himself as the alternative to Corzine. “Want to change Trenton? Start by changing governors,” was a familiar refrain in Christie’s primary campaign ads.

But even though hypothetical general election matchup polls showed Christie leading Corzine, the incumbent can hardly be counted out. New Jersey in recent years has trended strongly Democratic, going with the party in the past five presidential elections, including the 2008 contest in which Barack Obama received 57 percent of the vote to 42 percent for Republican John McCain . Democrats currently control the state legislature, both U.S. Senate seats, and eight out of 13 U.S. House seats.

Vice President Joseph R. Biden Jr. , a familiar figure to many in New Jersey from his previous 36-year tenure as senator from neighboring Delaware, helped Corzine kick off his general election campaign Tuesday night in West Orange, a New York City suburb. And President Obama can be expected to weigh in on behalf of Corzine and the effort to keep the governor’s seat in Democratic hands.