In a moment that's become almost as big a presidential milestone as the inauguration itself, George W. Bush celebrated the opening of his presidential library and museum today, which is opening the floodgates for historical judgements on his eight years in office. 

Officially, it's the dedication ceremony of "The George W. Bush Presidential Library and Museum and the George W. Bush Institute at the George W. Bush Presidential Center," which is on the campus of Southern Methodist University in Dallas. It's the third presidential library to be built in Texas.

Bush has spent most of this week previewing the center for the media, appearing in interviews with Diane Sawyer, Matt Lauer, John King, Charlie Rose, and many others, including a two-part special on Fox. Like all presidential museums, it's both an archive of documents and artifacts from his tenure and a chronicle of world events that happened during his presidency. One of the most talked about features is an interactive exhibit that confronts visitors "with the stark choices that confronted the nation's 43rd president" and forces them to make those decisions for themselves (with a ticking clock urging them on).

As for today's ceremony, the highlight for history watchers is the rare gathering of all the living Americans presidents, including the current one and Bush's own father. (Could there also be two future presidents in attendance in Hillary Clinton and Jeb Bush?) All five presidents are expected to speak, while the media will spend the day pouring over the Bush legacy and occasionally re-configuring long-held opinions of No. 43. As presidential historian Douglas Brinkley puts it, when you construct your library, "You're running for history instead of office."