Khan was elected Mayor of London at the 2016 mayoral election, defeating the Conservative candidate Zac Goldsmith, and resigned as an MP. As Mayor, he implemented the Hopper fare for unlimited bus and tram journeys for an hour, increased the cost and the area covered by the London congestion charge, and introduced new charges (the ULEZ and the T-Charge) for older and more polluting vehicles driving in the city. He also backed expansion at London City Airport and Gatwick Airport. He was a vocal supporter of the unsuccessful Britain Stronger in Europe and People's Vote campaigns for the UK to remain in the European Union, and attracted international attention for his Twitter arguments with United States President Donald Trump. He established the Commission for Diversity in the Public Realm following the 2020 George Floyd protests. Although Khan initially froze some Transport for London (TfL) fares, he has implemented transport fare rises since 2021 in return for a £1.6 billion bailout from the UK Government during the COVID-19 pandemic. He was re-elected as Mayor in May 2021, defeating the Conservative candidate Shaun Bailey.