You can’t miss the peak of Beto O’Rourke’s 2018 Texas Senate campaign in HBO’s “Running with Beto.” Maybe you’ve already seen it, on your phone or in a Facebook post: Mr. O’Rourke responding passionately to a question about N.F.L. players taking a knee to protest racism and police brutality.

When the former congressman begins his answer, our vantage point is in the room with him. But then the film’s perspective pulls back to the frame where it mattered most — the screens of social media apps, where the video racked up views and praise, visualized here in Likes and adulatory tweets that flutter onto the screen like a hosanna of rose petals, leading in turn to a slew of TV bookings.

That election was barely half a year ago, but the elegiac, fly-on-the-wall film, airing Tuesday, already feels like a document of another era. Since his much-covered near miss in November, Mr. O’Rourke has joined the teeming race for the White House, his story line being rewritten from Great Resistance Hope to vision-questing presidential Pippin, climbing on countertops to search for his corner of the sky.

But “Running with Beto” — a special about a social-media-driven campaign, co-produced by the Dem-friendly polititainment empire Crooked Media — is also an example of the very of-the-moment challenge of running for office in the Trump era. To pitch yourself as a president, you must first prove yourself as a show.