What did Hillary Clinton know about former aide Sidney Blumenthal’s toxic anti-Obama innuendoes and when did she know it? That question emerged from a day of back-and-forth between the Republican and Democratic nominees for president Friday.

GOP nominee Donald Trump is known to have helped spread the conspiracy theory known as birtherism. Birthers alleged that President Barack Obama, among other things, was not born in America and did not qualify as a “natural born citizen” for the purposes of serving as president.