As he barnstormed towns, live-streamed his travels and spoke with his signature gusto, Mr. O’Rourke captured the imagination of Democrats in deep-red Texas and across the nation. He came within three percentage points of pulling the upset , and talk of a presidential campaign soon followed.

2. What’s this about him being in a band?

Mr. O’Rourke chose to go to Columbia University in part because he looked up to his uncle, who had tapped into New York’s music scene. At the time, he went by Robert — Beto was a nickname from El Paso — and he played the guitar. He and a few of his friends formed a punk rock group.

After returning home to El Paso, Mr. O’Rourke quickly transitioned from musician to businessman, using a loan from his parents to create a web design company and an online newsmagazine. His brief tenure as a publisher prompted his interest in civic issues and he joined various local organizations. Mr. O’Rourke was elected to the El Paso City Council in 2005; he won his seat in Congress seven years later.