Even before the Sept. 11 attacks and the crackdown that followed, American Muslim leaders generally had come to believe they had made a mistake. In 2000, they made their first unified endorsement in a presidential race, backing George W. Bush. Many thought he would take a harder line against Israel, and, based on statements he made while campaigning, would protect the rights of immigrants facing deportation. Muslims say they were disappointed on both counts. Now, feeling the additional sting of being scrutinized in the domestic hunt for terrorists, they are mobilizing to express their anger at the polls in 2004....