WASHINGTON - With hundreds of thousands of supporters of immigrant rights taking to the streets in Los Angeles and other cities, activists have grown optimistic that the Senate will produce legislation allowing America's estimated 11 million undocumented aliens to stay and work in the U.S. But instead of claiming victory, many say they're already looking ahead to the next major battle: Closed-door meetings in which lawmakers will have to merge a Senate bill that includes a guest worker provision with a House version that does not. And some say that with midterm elections looming, the end result may be no...