Reagan’s marriage to Jane Wyman was invalid. When Wyman became a Catholic, her marriage to Reagan was declared null, because she was married to someone else first. Which means that, in the official eyes of the Catholic Church, Reagan’s marriage to Nancy was the first marriage for Ronnie and Nancy. Not that they cared, since neither one was Catholic.
In the eyes of the law, it was perfectly valid. Wyman dumped him which makes his situation much different from that of McCain, who came home from POW camp to a faithful wife who had been been in a terrible car accident. McCain looked and found a second wife with enough family money to launch a political career. The DBM will let you know all about it if he gets the Republican nomination. IMHO they are salivating with all they have to throw at McCain if he's the nominee.