Many loved ones of the nearly 3,000 people killed will join dignitaries and politicians at commemorations Thursday in New York, at the Pentagon and in Shanksville, Pennsylvania.

In a video statement, Trump said Kirk's death was a direct consequence of people demonizing those they disagree, and then turned his ire to the political left.

Kirk, the founder of Turning Point USA, was arguably the most influential voice in young conservatism, and played a pivotal role in President Trump's return to the White House.