The lead contractor on the dysfunctional Web site for the Affordable Care Act is filled with executives from a company that mishandled at least 20 other government IT projects, including a flawed effort to automate retirement benefits for millions of federal workers, documents and interviews show.

CGI Federal, the main Web site developer, entered the U.S. government market a decade ago when its parent company purchased American Management Systems, a Fairfax County contractor that was coming off a series of troubled projects. CGI moved into AMS’s custom-made building off Interstate 66, changed the sign outside and kept the core of employees, who now populate the upper ranks of CGI Federal…

A year before CGI Group acquired AMS in 2004, AMS settled a lawsuit brought by the head of the Federal Retirement Thrift Investment Board, which had hired the company to upgrade the agency’s computer system. AMS had gone $60 million over budget and virtually all of the computer code it wrote turned out to be useless, according to a report by a U.S. Senate committee.