The US Federal Bureau of Investigation said on Sunday it was investigating an incident in which a convoy of vehicles flying flags in support of President Donald Trump’s re-election bid surrounded a tour bus carrying campaign staff for Democratic challenger Joe Biden on a Texas motorway. The bus was travelling between San Antonio and Austin, Texas on Friday when pickup trucks and other vehicles flying Trump 2020 flags drove near and around it. Neither Democratic presidential challenger Joe Biden nor his running mate, Senator Kamala Harris, were aboard the bus, though it was carrying campaign staff. The Biden campaign said they called the emergency services and local law enforcement assisted the bus in reaching its destination. President Trump took to Twitter in response to the FBI announcement, saying "In my opinion, these patriots did nothing wrong". Earlier in the day, while campaigning in Philadelphia, Mr Biden commented on the events: "We've never had anything like this. At least we have never had a President who thinks it's a good thing." The motorway confrontation came as polls showed an unexpectedly tight race between Mr Biden and Mr Trump in Texas, which has long been a Republican stronghold.