WASHINGTON -- Only in the arcane world of the U.S. Senate could a quirky gambit known as a "clay pigeon" make the difference between passage of an important immigration measure and its death at the hands of opponents. Democratic leaders hope the complex maneuver _ which makes use of the Senate's labyrinthine rules to insist on votes on amendments _ will frustrate conservatives' attempts to derail the embattled immigration bill, instead putting it on a fast track to passage next week. Majority Leader Harry Reid, D-Nev., said he would revive the bill to legalize as many as 12 million unlawful...