Last night, former Texas Rep. Ron Paul gave a 51-minute speech to young libertarians in Washington. He talked about the collapse of Greece's economy, the Cold War, the military draft, the works of Frederic Bastiat, and the many faults of the Federal Reserve. He did not mention his son, Sen. Rand Paul (R-Ky.) -- even when it sounded like he might.

"I think there's a presidential election coming up," Paul joked late into the speech. "Am I a candidate this year? No, I'm not!"

After the laughter from 300-odd Young Americans for Liberty activists died down, Paul cited "two individuals right now that have sort of caught the attention." Neither was a relative. "One of them is way over on this side -- I don't know where to put him, but he's not on the libertarian side. He's making a lot of noise. That's a guy named Trump. The other is named Bernie Sanders," he said.

The Daily Beast's Olivia Nuzzi, one of very few reporters who covered the speech live, called Paul's speech a "passive aggressive" knock on his son. It also put him at odds with his audience. Paul had been introduced by Jeff Frazee, a former intern in his congressional office who went on to co-found and lead Young Americans for Liberty. Just last month, Frazee took a key role in a super PAC, Concerned American Voters, dedicated to electing Rand Paul -- and many of its organizers are YAL veterans.

But the elder Paul has kept a careful distance from his son's campaign. In February, when he participated in a Q&A at the international Students for Liberty conference, Paul joked that he was still weighing whether to vote for his son. "I'm seriously thinking about it," he said. "I'm studying his record." His patter was indistinguishable from a parody in The Onion, in which Paul was still waiting for a "true libertarian" to enter the race.  CNN's Michael Smerconish is one of the few reporters to coax a Rand Paul comment out of Ron Paul this year, prodding the elder statesman of libertarianism to say that his son was "the only one that, from my viewpoint, is talking any common sense." In the same interview, Ron Paul confirmed that he would not be stumping for Rand Paul.

The detente between the Pauls was hard-won. Since retiring from the House in 2013, Ron Paul has launched a think tank, a Web series, and at least one financial advice venture. For a long time, the surest way to irritate Sen. Paul was to ask for a reaction to what Rep. Paul had said or done. In April, the senator criticized Russia's incursions into Ukrainian territory following the fall of that country's government; the former congressman said that "the Ukraine coup was planned by NATO and EU."

Since then, father and son have continued to disagree, but the press has moved on. Buzzfeed's indefatigable Andrew Kaczysnki has continued to track Ron Paul's commentary, and singled out gaffe-shaped remarks about military "dupes" and "false flag" economic crises. There's no sign the younger Paul has not been asked about any of this. Kaczynski was one of the few reporters to cover the July 17 release of Ron Paul's new foreign policy treatise, Swords to Plowshares; if Rand Paul has been asked about the book, none of the answers have been printed.

At the YAL conference, Paul's riff on the nuclear agreement with Iran highlighted another contrast with his son. He backed the deal; Rand Paul did not.

"To say that the Iranians aren't perfect people, and we shouldn't talk to them -- you know, we have been so obsessed that they're going have a nuclear weapon in one week, one month, one year," said Ron Paul. "So obsessed on a weapon that doesn't exist. The Soviets had 30,000 of them. And they tell us we're a bunch of kooks for wanting to talking to them? I'd say the lesson is that friendship is a wise idea."