Two years ago, Coakley was political Kryptonite. The Democrat who lost Ted Kennedy’s seat to a little-known Republican wasn’t expected to have a political future, much less a rising one. But following her reelection win as attorney general 10 months after losing the Senate seat, she beat her way back to grudging respect. And when her office brought criminal charges against former treasurer Timothy P. Cahill, some questioned her political motives, thinking they spied an opening salvo in a new campaign.