President Joe Biden briefly wore a red Trump campaign hat at an event commemorating the 23rd anniversary of the 9/11 attacks, the BBC reports.
He was visiting firefighters in Pennsylvania near where one of the four hijacked planes crashed, and the White House said he donned the cap as a gesture of unity.
Video recording the incident shows the president having a friendly conversation with a Trump supporter before they swap headwear.
Donald Trump’s campaign was quick to see the funny side. “Thanks for the support, Joe!” one post read with a photo of Biden in the trademark Republican hat.
Another said “Kamala did so bad in last night’s debate, Joe Biden just put on a Trump hat”.
The event in Shanksville commemorated Flight 93, which was hijacked by terrorists in 2001.
Passengers aboard the flight fought back and prevented a plan by al-Qaeda to crash the plane into a government building in Washington, DC. All 40 aboard died.
Biden greeted firefighters and paid respects at a cross made from the broken fusilage.
