We've just learned that MoveOn is about to sink half a million dollars into a huge ad buy in North Carolina linking Elizabeth Dole, who's facing a tough re-election fight, to John McCain and Big Oil. Here's a first look at MoveOn's spot, which will run statewide starting tomorrow night:The ad, which highlights GOP support for tax breaks for oil companies, will be released sometime today in honor of McCain's high-profile trip to an oil rig.It's likely that the spot foreshadows more ads from MoveOn linking GOP Senate incumbents to Big Oil and McCain. Though some polls show public preference for McCain's position on drilling, MoveOn and Dems believe that hammering away at the links between the GOP and the big oil companies can change the conversation in their favor.