IN SEPTEMBER of 2011, a fortyish budget connoisseur named Maya MacGuineas was feeling demoralized. She couldn’t believe that Congress and the president had nearly let the country default on its debt rather than reach a major deficit-cutting deal the previous summer. So she did what she had become unofficially famous for in the wonk circles of Washington: She threw a glamorous dinner party. MacGuineas’s friend, Virginia Senator Mark Warner, agreed to open his Alexandria estate to a coterie of bold-faced names.