In campaign funding, “‘Incumbents almost always outraise the challengers,’ said Anthony J. Corrado, a campaign finance expert at Colby College. “What is notable this year, Corrado said, is that Democratic challengers have enough money to stage full-fledged efforts, and that is one reason the election appears to be so close. ‘Although they haven’t matched the incumbents,’ he said, ‘challengers are raising the amounts of money that they need to be competitive.’