Having met David Letterman and Jay Leno only briefly, I’d normally hesitate to put them on the couch. But hey, watch someone on TV long enough and you feel like you know them.

In his heart of hearts, Letterman has never been able to fathom or accept that Leno rebounded to emerge as the latenight ratings champ. The nagging weight of that indignity could be seen in NBC’s recent press release highlighting Leno’s dominance through the 2007-08 broadcast season (No. 1 for 13 years in a row; an average advantage of 1.2 million viewers, etc.), crowing about “The Tonight Show” even though the host’s future plans probably don’t include NBC.

For his part, Leno — despite the good-sport, aw-shucks attitude — will never entirely grasp why Letterman is widely preferred by critics and the intelligentsia, who tend to dismiss his monologue-driven show as commercially successful, but creatively disposable.

Enter Letterman’s injection into the presidential race last week, which delivered a stark demonstration of why Dave has enjoyed teacher’s pet status. Although seldom invoked anymore, it’s as simple as the distinction between a comic (even an admirably hard-working one) and an old-fashioned broadcaster, predicated on Letterman’s ability to create his show at the desk in a manner Leno — still more natural as a standup than a talkshow host — never could.

Much has been stated about Letterman’s virtuoso mix of comedy and righteous indignation after GOP presidential nominee John McCain’s last-minute “Late Show” cancellation, insisting (falsely, as it turned out) that he needed to rush back to Washington because of the financial crisis. Little of the commentary, however, has adequately characterized why the tongue-lashing Letterman administered was so remarkable — a barrage of jabs that MSNBC’s Keith Olbermann (who had a front-row seat for the tirade) described as “perhaps the sharpest, certainly the most persistent political satire of the campaign.”

BEFORE THE BUSH presidency, Letterman emulated his idol Johnny Carson and was never really overtly political. In the past, he exhibited obvious respect and affection for Republicans like Bob Dole and McCain, while gleefully joining in jokes about the Clintons, especially Bill’s seemingly unquenchable appetites.

Gradually, though, the Bush administration’s missteps — including the president’s lack of oratorical eloquence (a trait Letterman memorialized with the recurring feature “Great moments in presidential speeches”) — and the mounting toll of the Iraq war prompted more open disdain. It was this altered mentality that caused Letterman to backhand guest Bill O’Reilly in 2006, telling the surprised Fox News host, “I’m not smart enough to debate you point to point on this, but I have the feeling about 60% of what you say is crap.”

Already inclined to see any rebuke as a “vile smear,” O’Reilly subsequently explained away Letterman’s slight by labeling him a “far-left guy.” In fact, it’s precisely because he’s traditionally not an ideologue that Letterman’s broadsides have felt like a more sobering indictment. Bush’s incompetence and McCain’s apparent desperation have spurred him to dispense with the customary Carsonian objectivity.

BY CONTRAST, it’s hard to envision Leno taking such a stand, even if Letterman’s motivation combined principle with a plain fit of pique. Hell, barring a few jocular swipes Leno has stayed graciously silent about NBC despite the awkwardness of his situation, as suitors circle him when he passes “The Tonight Show” baton to Conan O’Brien next year.

What we’re actually seeing is the end of an era, moving beyond choosing the popular guy (Leno) or the respected one (Letterman) to a handful of chirpy voices. Indeed, ratings notwithstanding, the election run-up has further ensconced “The Daily Show With Jon Stewart” as latenight TV’s most sophisticated voice — providing nightly cranial massage to an audience rightfully dismayed by the emptiness of most TV talk and news.

Yet after what almost literally amounted to his wake-up call from McCain, Letterman briefly reminded those weaned on his show what distinguishes him from Leno — and why the latenight throne has remained divided since Carson’s departure, with each host claiming half the crown.

As for the reshuffling of latenight jokers, don’t expect that campaign to produce a clear winner; instead, look for the two-party system to break down into a parliamentary free-for-all.