The vote was close. A cluster of senators from both parties, authors of the immigration bill under debate, hovered over the clerk tallying the votes on an amendment that could bring down their fragile compromise legislation. At 45 to 45, Arizona's Jon Kyl, the lead Republican architect of the bill, put his hand to his chin. At 48 to 45, he crossed his arms and bit his lip. Ken Salazar, the Colorado Democrat who helped write the bill, leaned in. The count stopped: 49 to 48. The amendment had passed, and their bill looked doomed. The bipartisan team sprang into...