Like a lot of people, I find my television habits have changed a great deal over the past few years. I watch less and less of the main networks and less cable in real time, and I absorb a growing proportion of my TV from online snippets. If something funny or interesting or sharp happened on television last night, I’ll tend to catch it on YouTube the next day. The blogs fill me in.

But there is one hour of television I tend to watch nightly, and I’m not the only one. Although I’m a news junkie and spend my day glued to the internet, it still provides information I haven’t yet seen, interviews big political figures in probing and sometimes revealing ways and charts the evolving cultural zeitgeist for the underforties. It also, I hasten to add, reliably makes me laugh.

The hour on the Comedy Central cable channel between 11pm and midnight has become for today’s American political culture what That Was the Week That Was once was in British public life. It is anchored by Jon Stewart, a former stand-up comedian who hosted the Oscars last year, diminutive, more Jewy than Jewish and buttressed by an array of young talent posing as parodies of television news correspondents. They have had a “senior Palestinian analyst” and a “senior child-molestation expert”. Segments range from This Week in God to a recurring feature on the Iraq war, Mess O’Potamia. Yes, they love puns.

At 11.30pm, the talent cedes to genius as a former Daily Show correspondent, Stephen Colbert, hosts a spin-off show, The Colbert Report, that is a parody of the various one-man right-wing opinion shows that crowd the evening hours on “serious” cable. Watching these shows - The O’Reilly Factor is the most compulsive - induces in a viewer a form of retching nausea. I watch O’Reilly out of morbid fascination, even though the relentless demagoguery, creepy smiles and deadpan assertion that viewers are entering a “no-spin zone” can leave one somewhat depleted.

For years, one felt dumb for arguing back and dumber for failing to change the channel. And then Colbert came along, several hours later - with a parody as lovingly accurate as all great parodies are. The show’s graphics include countless American flags and a swooping, screeching eagle; the regular features include an ominous “Threatdown” of dangers facing the American people, and a daily harangue called The Word. In style and substance, Colbert has mastered the art of total and absolute certainty regardless of the facts that has become a hallmark of the Bush era. Before long, after all, if you don’t cry, you feel the need to laugh.

Colbert even invented a new word that became 2006’s word of the year, according to the Merriam-Webster dictionary: “truthiness”. It’s the truth according to the gut instinct of the president.

Here’s how Colbert explained it: “I don’t trust books. They’re all fact, no heart. And that’s exactly what’s pulling our country apart today. ’Cause face it, folks: we are a divided nation. Not between Democrats and Republicans, or conservatives and liberals, or tops and bottoms. No, we are divided between those who think with their head and those who know with their heart . . . What about Iraq? If you think about it, maybe there are a few missing pieces to the rationale for war. But doesn’t taking Saddam out feel like the right thing?” If you want a pitch-perfect parody of Bush conservatism, it’s hard to beat.

You can appreciate the programme’s clout when you look at the guest lists. In the past fortnight, Stewart’s cable show at 11pm has managed to secure, among others, the former Mexican president Vicente Fox, Dick Cheney’s wife, Lynne, Jake Gyllenhaal and Meryl Streep.

But the bipartisan guest list cannot disguise the anti-establishment, liberal bent of the show. Yes, Stewart and Colbert rib the Democrats. Their coverage of the 2004 primaries was framed with the title “The Race from the White House”. But with Bush in charge of things, the targets for liberal humour have been unusually plentiful.

Stewart skewers Bushism directly; Colbert achieves his edge by out-Bushing Bush. He does so with total deadpan sincerity, almost never breaking for a second out of character. My first time on the show, he sat me down and posed the first question: “How old were you when you chose to be gay?”

Last year, the White House Correspondents’ Association made the mistake of asking Colbert to be guest of honour at its annual dinner. Colbert saw an opportunity. As an improv star from Chicago’s Second City theatre – the theatre that gave America John Belushi, Mike Myers and Bill Murray – he played it totally straight and totally fearless, looking directly at a thoroughly unamused president and declaiming: “I stand by this man. I stand by this man because he stands for things. Not only for things; he stands on things. Things like aircraft carriers, and rubble, and recently flooded city squares. And that sends a strong message: that no matter what happens to America, she will always rebound with the most powerfully staged photo ops in the world.”

The Washington crowd was appalled. The internet loved it.

With 1.4m viewers nightly, the Colbert-Stewart combo does not match the large, ageing viewership of the networks, but, as any marketeer knows, it’s the quality of the demo-graphic that counts. The Daily Show hour manages to bring in more men in the 18-34 age bracket than almost anything else on television. If you go to any college campus in the country, it is the favourite show.

Its power in the marketplace is felt elsewhere, too. Last week, Colbert’s book I Am America (And So Can You!) leapt instantly to the top of the sales charts, ahead of Bill Clinton, Clarence Thomas and Alan Green-span. To cap it off, he declared his intention to run for president in his home state of South Carolina. He meant it. And even The New York Times had to cover the story.

This moment will pass, of course. One gets a sense that it may be peaking already. For satire to work well, it has to let off the collective steam of a nation. It needs a po-faced, Cheney-style establishment to mock. As the religion-drenched era of Republican hegemony wanes a little, the satirists begin to become part of the establishment themselves. Colbert’s presidential run may be a step too far. Perhaps, in retrospect, these last, ragged months of the Bush administration will come to seem the high-water mark of the Colbert-Stewart tide. But it’s been a joy while it’s lasted.

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