Bush and Clinton spoke at the dedication of the first phase of the memorial last September, with BoehnerJohn Andrew BoehnerZeal, this time from the center Juan Williams: The GOP's deal with the devil Hillicon Valley: Trump hits China with massive tech tariffs | Facebook meets with GOP leaders over bias allegations | Judge sends Manafort to jail ahead of trial | AT&T completes Time Warner purchase MORE also in attendance. The dedication marked the transition from a temporary to a permanent memorial for the site, a field where the United 93 airliner crashed after it was hijacked on Sept. 11, 2001. According to the Park Service, one third of the memorial construction is now complete.

At the time, Clinton pledged he and Boehner would follow through to help raise funds the remaining $10 million needed to finish the memorial. The memorial plans include a learning center and a "Tower of Voices" containing 40 large wind chimes representing the 40 lives lost when the plane crashed.

Boehner tweeted Monday that he is "proud to be working with Presidents Bush & Clinton to raise funds."

Bush signed the Flight 93 Memorial Act into law in 2002, creating a new national park to commemorate the crew and passengers of the flight. United Flight 93 likely would have been flown into the U.S. Capitol during the 9/11 attacks had passengers not fought the hijackers and ultimately caused the plane to divert and crash in Pennsylvania.

In their speeches last September, Bush and Clinton credited the civilians on the plane for what Bush called the "first counteroffensive of the war on terror."