Charlie Kirk, the 31-year-old conservative activist and firebrand, developed an enormous following, particularly among young people, for his brash, unapologetic positions on social issues.

The investigation continues into the circumstances of his killing on Wednesday at a Utah campus event, including who the shooter was and what their motivations were.

But his death has reignited a debate about political violence and polarization in this country.

While many politicians have expressed remorse and condemnation for the killing, social media has been riven with factional debates. Some on the left have celebrated and joked about his death. Some on the right have blamed Democrats or liberals and have vowed revenge.

But how did Charlie Kirk, at such a young age, amass so much political influence and the friendship of the sitting president?

Today, Explained host Noel King discussed this with Kyle Spencer, journalist and author of Raising Them Right: The Untold Story of America’s Ultraconservative Youth Movement and Its Plot for Power.

Charlie Kirk was one of the young people she profiled in that book, and in writing it, she got to know him.

Below is an excerpt of their conversation, edited for length and clarity. There’s much more in the full podcast, so listen to Today, Explained wherever you get podcasts, including Apple Podcasts, Pandora, and Spotify.

Charlie Kirk was a central character in your book Raising Them Right. Tell me about him.

Charlie was a very, very charismatic leader of the modern Republican Party. He started out as a kid who cared about politics and morphed slowly into somebody who was able to transform the way people thought about Republicans.

© Vox