U.S. Sen. Cory Gardner questioned Wednesday why President Donald Trump’s tweets are sometimes censored by Twitter but tweets from Iranian Ayatollah Ali Khamenei, including one denying the Holocaust, are not. The public questioning came during a hearing of the Senate Commerce Committee on social media regulations. Testifying were Twitter CEO Jack Dorsey, Facebook founder Mark Zuckerberg and Google CEO Sundar Pichai. Dorsey said he believes Twitter has removed or flagged tweets from Khamenei and other world leaders aside from Trump, but could not recall any examples.