In 2004 an as yet unknown Barack Obama delivered the keynote speech at the Democratic convention. Four years later he became president. 

Some believe history could repeat itself with Julián Castro, although he might have to wait eight years for it to happen.

Mr Castro, then the mayor of San Antonio in Texas, America’s, seventh largest city, was the keynote speaker at the party’s 2012 convention.

A couple of years later he was secretary of housing and urban development in Mr Obama’s cabinet. By 2016, he was a potential running mate for Hillary Clinton and now he is a 2020 presidential candidate.

"I’m running for president because it’s time for new leadership. Because it’s time for new energy,"…