WASHINGTON (Reuters) - Three top Senate Democrats said on Thursday they will vote against Supreme Court nominee Samuel Alito because they fear he would not provide an effective check to what they described as President George W. Bush's bid for expanded power. While Alito appeared headed toward confirmation by the Republican-led Senate, Sens. Patrick Leahy of Vermont, Dick Durbin of Illinois and Edward Kennedy of Massachusetts made the case against Bush's 55-year-old conservative candidate. They expressed concern that if confirmed, Alito, a federal appeals judge since 1990, would push the nation's highest court to the right on a number of...