TRENTON, N.J. (AP) — New Jersey Gov. Chris Christie isn't joining the GOP field running for president in 2012, but he may have a hand in shaping the race from the sidelines.Political operatives say Christie's network of admirers, his big-money donors and his continued popularity would make his endorsement a coveted campaign contribution.GOP political consultant Phil Musser, a senior adviser for former Minnesota Gov. Tim Pawlenty's presidential campaign, says a Christie endorsement will be "aggressively sought after."If some candidates were annoyed that Christie sucked up the media spotlight for a week as he again considered joining the race, Christie says they haven't told him so. He isn't tipping his hand to endorsements yet, but on Tuesday he said he'll work hard for the eventual Republican nominee.