WASHINGTON (AP) - For the first time in nearly two decades, the federal government staggered into a partial shutdown Monday at midnight after congressional Republicans demanded changes in the nation's health care law as the price for essential federal funding and President Barack Obama and Democrats refused. As Congress gridlocked, Obama said a "shutdown will have a very real economic impact on real people, right away," with hundreds of thousands of federal workers furloughed and veterans' centers, national parks, most of the space agency and other government operations shuttered.