The White House was knee-deep in budget negotiations with Republican lawmakers one May afternoon when Senate Democrats boarded buses for a short ride down Pennsylvania Avenue for a face-to-face session with President Obama. Seated in an auditorium, the senators pressed Obama on their key concern as talks heated up over raising the nation’s debt ceiling: How would he stand up to tea party Republicans? To the dismay of many in the audience, Obama conceded that he probably couldn’t — and probably wouldn’t — push too hard because he was unwilling to risk a U.S.