The DFL candidates for Governor took aim at Attorney General Skip Humphrey last night in the final debate of the primary campaign. Humphrey is leading in the polls, but his lead has shrunk a little. Now the other four candidates are looking for opportunities to bring him down further. Minnesota Public Radio's Martin Kaste reports: It's a rule of thumb in politics that if you're trying to identify the front-runner in a race, you should look for the candidate who's deflecting the most attacks. At the DFL gubernatorial debate sponsored by MPR last night, that person was Skip Humphrey. Ted Mondale threw the first punch by accusing Humphrey of being too ready to promise more tax cuts and programs than the state can afford.