You may have the misfortune already to be aware that Donald Rumsfeld, America's favourite warmongering uncle, is currently on a US-wide book tour to promote his memoir, inevitably titled Known And Unknown, which was published last month. Unlike other ventures with which the former secretary of defence has been associated in the past, this publicity assault doesn't seem to have followed the Rumsfeld doctrine of "light force" warfare, nor demonstrated a reckless disregard for proper planning. On the contrary, it's a carefully calculated, heavy artillery barrage that has turned an 832-page meditation on his career in politics (short version: it was splendid, thanks for asking!) into a number one New York Times bestseller.

So far, so annoying. You might think, at least, that the resurfacing Rumsfeld would have faced some vigorous satirical evisceration at the hands of, say, Jon Stewart of The Daily Show. Unfortunately, you'd be wrong.

For half a decade now – the landmark poll was in 2006 – we've been hearing how news comedy, epitomised by The Daily Show, has replaced traditional outlets as the primary source of news for younger Americans. But Rumsfeld's promotional tour underscores the limits of the form. It may go down as the moment when the usual victims of Stewart-style satire figured out how to turn it to their advantage.

Treading where neither George Bush nor Dick Cheney had gone before, Rumsfeld visited the Daily Show studios for an interview with Stewart. And despite the host's opening gambit – "I think I know why you're here, and let me just deflate the tension right off the bat: apology accepted." – he chuckled and question-dodged his way to an easy victory. ("Just wrapped up one of the most thoughtful interviews of book tour," his Twitter feed observed.)

A radio run-in with the comedian Louis CK unfolded similarly. "There are people who believe, literally, that [you and Cheney] are lizards from outer space who eat human flesh," Rumsfeld was told. "I don't know if anybody's ever asked you directly, sir, but are you a lizard person?" In certain quarters, this line of questioning – it developed into reflections on Rumsfeld's alleged predilection for "eating Mexican babies" – was denounced as deeply disrespectful. But of course it was anything but. It stuck in the craw – as, doubtless, do babies – precisely because the result was, for Rumsfeld, such an easy ride.

(The funniest part wasn't Louis CK's questioning but Rumsfeld's inadvertent demonstration of his apparently congenital inability to answer any question straightforwardly: even on the subject of whether or not he was a space-lizard, he gave no direct answer.)

Stewart is the first to point out that he's a comic, not a reporter, and Louis CK wasn't pretending otherwise, either. Their first priority is provoking laughter, and that's as it should be: anyone even slightly familiar with left-wing British comedy is all too aware of the dull hectoring that results when the politics starts to outweigh the jokes. But the publicity swing for Known and Unknown demonstrates the futility of relying on comedians to hold politicians to account. And it suggests a simple strategy for those in Rumsfeld's position in the future: chortle along gamely and there's pretty much no way you can lose.

Trump for president?

According to numerous reports, Donald Trump is taking the prospect of a presidential run next year "seriously", which brings the number of people taking the idea seriously to at least one, along with any minions he may be paying to do likewise. The news that an opinion poll commissioned by Newsweek puts him two points behind Barack Obama in a theoretical head-to-head contest is no reason to imagine his notion is gaining traction: one suspects it just shows that opinion-poll respondents have a sense of humour.

Let me go out on a limb here: Donald Trump will not run for president. If he does, I will watch an entire season of his version of The Apprentice back-to-back on DVD while drinking one of his new range of "mood infusion beverages" and wearing a toupee.

"Most people out there think this is a joke – that I'm doing it for publicity," he told the MSNBC host Joe Scarborough. "Imagine what happens the day I announce I am actually running for president!" Indeed! Imagine! And imagine hard, because on this subject imagining is all you'll ever get to do.

Trump periodically "mulls" a presidential run, as he did in 1988 and 2000, because "he loves attention and to be treated fawningly", as Jamie Poniewozik put it on Time magazine's website. What he does not like is "losing, humiliation and being made to look bad publicly". The ceaseless effort Trump invests in burnishing his personal brand is far from incidental to his business: his credibility as a property tycoon depends on it. Unlike numerous deluded presidential no-hopers, Trump knows exactly what he's doing. But running for president isn't it.

Another reason it won't happen: Trump is a germophobe who hates shaking hands. "One of the curses of American society is the act of shaking hands, and the more successful and famous one becomes the worse this terrible custom seems to get," he wrote in his 1997 book The Art of the Comeback. "I happen to be a clean-hands freak. I feel much better after I thoroughly wash my hands, which I do as much as possible." There's little point readying the "You're Fired!" headlines for when Trump's presidential efforts fail. He isn't really applying for the job.