The Federal Bureau of Investigation investigates an incident involving Trump supporters swarming a Joe Biden campaign bus as it traveled from San Antonio to Austin Saturday.

According to CNN, staffers on the bus called 911 after nearly 100 vehicles blockaded the tour bus on the interstate and tried to run it off the road.

On Sunday, Trump said his supporters were "protecting" the bus, according to Forbes.

A Biden campaign staffer told CNN Saturday's incident involved nearly 100 vehicles.

Neither Former Vice President Joe Biden nor California Sen. Kamala Harris were on the bus, CNN reported.