President Joe Biden wore a “Trump 2024” hat on Wednesday — and though it confused Republicans, he had a specific reason for doing so. The president was at an event in Shanksville, Pennsylvania, to mark the anniversary of the Sept. 11 terrorist attacks. Shanksville was the site of the United Flight 93 crash, in which passengers revolted against hijackers trying to fly the plane into a government building in Washington, D.C. Shanksville is in a small, conservative county where voters backed former President Donald Trump by a margin greater than 3 to 1, and many attendees were wearing Trump merch…