DENVER — Sen. Mark Udall (D-Colo.) and his allies have a clear message for political handicappers and pollsters: You’re wrong. The incumbent and his supporters insist they will shock the pundits on Election Day, even though Udall hasn’t had the lead in a single public poll in more than a month and is facing a rising GOP star in Rep. Cory Gardner. Two new surveys released Tuesday gave Gardner a narrow lead, underscoring Democratic fears that the race for the Senate majority could be lost in a state that voted for Barack Obama twice. Udall’s campaign scoffs at suggestions that...