As hundreds of thousands of motorcyclists gathered Sunday morning outside the Pentagon for the 25th annual Rolling Thunder ride into the District, Jim Bradley couldn’t help but marvel at the scene.

Mr. Bradley, a retired Air Force lieutenant, rode in his first Rolling Thunder 15 years ago and has come back every year since – each time leaving in awe of the boundless patriotism and sheer scale of the event, which is held to honor veterans, including prisoners of war and service members missing in action.

“It’s important that the people up on Capitol Hill know that it’s the politicians’ responsibility to account for everyone they send over there,”