Charlie Kirk, the founder of Turning Point USA, leveraged an audience of millions of fervent conservative fans and fierce liberal critics to create a youth-oriented movement on the right, emerging as one of the most prominent voices in the age of Donald Trump.

He specialized in debates - especially at college campuses - in which he took on liberal opponents, often creating moments that went viral and captured audiences across the political spectrum. It was during one such session Wednesday at Utah Valley University in Orem, Utah, that Mr. Kirk, 31, was shot and killed, sending shock waves through Trump’s base of supporters and beyond.

Trump confirmed Mr. Kirk’s death in a statement on social media, a sign of his importance to the president’s political movement.

He later recorded an Oval

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