Campaign Insider.

Douglas Holtz-Eakin knew the 2003 Boeing Air Force tanker deal was a rotten, overpriced plan, but he was not supposed to say so. As head of the Congressional Budget Office, he had a simple job: crunch numbers, avoid policy disputes. But one day at a September 2003 Senate hearing, John McCain asked him directly: Do you think the deal should be approved?

"No," Holtz-Eakin replied, as his staff released a collective gasp of horror. Eventually, the tanker deal collapsed under a cloud of scandal, further cementing the bond between the Arizona politician and the Princeton-trained economist. "He got me," says Holtz-Eakin, remembering McCain's question. "I liked that."

He liked it a lot. The economist has devoted almost every waking hour since July working as McCain's unpaid senior policy adviser. "It is the hardest thing I have ever done," says Holtz-Eakin, 50. "I can live for an extended period of time on Twizzlers and Diet Coke."

Under his guidance, the campaign has developed an economic plan focused on cutting federal spending, reforming entitlement programs and ending congressional earmarks. But McCain also wants to extend all of President Bush's tax cuts and enact a costly new one of his own, raising concerns among budget hawks. The former congressional bean counter, however, is confident that a balanced budget can be achieved by 2012. "That's the goal," he says.