Sen. Rand Paul’s filibuster last week placed the Kentucky Republican and Sen. John McCain, Ariz., on opposite sides of a generational divide in their party that goes beyond ideology.

That flared into an open spat as McCain hissed: “The country needs more senators who care about liberty, but if Mr. Paul wants to be taken seriously, he needs to do more than pull political stunts that fire up impressionable libertarian kids in their college dorms. He needs to know what he’s talking about.” That peevish retort may have reflected McCain’s sense that he had been badly upstaged. Or maybe he hadn’t followed the debate.

With near-perfect timing, Paul got his response in a two-sentence letter from Attorney General Eric Holder. The first sentence was dishonest: “It has come to my attention you have now asked an additional question: ‘Does the President have the authority to use a weaponized drone to kill an American not engaged in combat on American soil?’ ” In fact, that was Paul’s question all along. But Holder then admitted, no, the U.S. government doesn’t have the authority to target U.S. citizens at home who are not involved in hostilities.

Paul got to crow in a series of interviews. He had pried an answer out of a White House habitually averse to treating a co-equal branch with respect. He certainly got more done than McCain and his closest amigo, Lindsey Graham, R-S.C., did by attending a dinner with the president.

The lesson from the Paul episode for the right and for the left, and especially for the media, is that it pays to challenge the president to live up to his claim of overseeing the “most transparent administration in history.”

It is also a lesson for Republicans that cordial, forceful assertion of principle gets you attention and praise. If the hawkish right is looking for new, effective leadership, Rand Paul is not going to be their man, but McCain and Graham aren’t the future, either.