Congress’s failure to deliver major health care legislation by President Barack Obama’s deadline next month transforms the traditionally sleepy August recess into what could be the decisive moment in the battle to win support for the legislation, especially from conservative Democrats considered crucial to its fate. The recess, scheduled to begin August 7, will put to the test Obama’s vaunted, high tech political machine and the coordinated network of progressive groups that has been quietly preparing for months for this battle. They face, on the other side, a bruised Republican camp hoping to revive itself through a winning campaign against...