THERE ARE two television sets on my desk, one tuned to CNN, the other to the Fox News Channel. Spotting the difference between the two used to be an easy task. Fox would be showing an aerial shot of a beaten-up Chevy Suburban being pursued at 95mph by wailing police cars. The bottom of the screen would flash with the legend: “Junkie Dad On The Run”. Meanwhile, on CNN,a woman would be standing in smart business dress on the White House lawn.

Fox — which is owned by The News Corporation, parent company of The Times — was a brash upstart serving up greasy gobbets of tabloid sensationalism. The important stories of the day would be covered, not broken, while the breaking news would come straight from the crime blotter, with car chases a speciality.

CNN earned its stripes as the news channel of record during the 1991 Gulf War, with its groundbreaking live coverage of the first night of allied bombardment. But with another costly Gulf war in the offing, and media organisations all over the world reeling from a lengthy and deep advertising recession, its crown appears to have slipped. US prime-time viewing figures, compiled by Neilsen Ratings, show that in the third quarter of 2002 Fox led the cable news channels with 1.1 million viewers on average. CNN had 800,000, while MSNBC was way behind with 200,000. In the same period a year earlier, CNN had 1.3 million viewers, Fox had 900,000 and MSNBC had 500,000.

The year or more of decline at CNN happened to coincide with the year-and-a-half that Walter Isaacson, a respected journalist and former editor of Time magazine, served as chairman of the cable news company. He resigned on Monday.

As a dyed-in-the-wool newsman, Isaacson believed that CNN would prosper by sticking to traditional news values, and that showbiz should stay in Hollywood. Events helped his strategy to succeed at first, with the September 11 attacks and the ensuing war in Afghanistan. But those developments also allowed MSNBC, Fox and the other networks to show that they had learnt from CNN’s Gulf War success and could also turn events into exciting 24-hour news coverage.

So Isaacson tried his hand at showbiz, hiring Connie Chung from ABC and Paula Zahn from Fox. He waved the chequebook around, too, taking Larry King back to CNN on a $7 million (£4.4 million) multi-year deal. Still the ratings slipped — but he refused to engage in a full-on ratings battle with Fox.

“It wasn’t in my nature to get into public p***ing matches,” he told The New York Observer after his resignation. “Maybe that was wrong. But if you engage them in a two-way fight, you allow them to determine the battlefield.”

Yet his Fox counterpart, Roger Ailes, went to war anyway, defining the battlefield from the start. Ailes is a former political consultant who masterminded election strategy for the Republican Party.

Tom Wolzien, a media analyst and former NBC executive, says: “I have great admiration for what Roger has done at Fox. He won the ratings battle like he would an election. He consolidated the right, then shifted to the centre.”

In short, Ailes brought opinions to the news at Fox: the right-wing opinions that appeal to the broad band of middle America but which are alien to the New York, Los Angeles and, in CNN’s case, Atlantan, sensibilities that tend to dominate the US news media.

Fox News anchors chat among themselves about their feelings towards a particular story, and show their patriotism at every turn. America is commonly referred to as “us” or “we”, and even bilateral peace talks are covered as if a football game were under discussion.

Then Ailes brought in two star presenters who are anything but conservative, in the form of Greta Van Susteren and Geraldo Rivera — representing a shift to the centre to bring in the East and West-Coast viewers and avoid accusations of political skew.

“Roger Ailes saw a niche, carved it out and progressively expanded it,” says Charles Bierbauer, former chief Washington correspondent for CNN and now dean of the school of mass communications and information studies at the University of South Carolina.

Ailes brought game-show showmanship to the news — on Fox last night, every story was accompanied by graphics that went “swoosh” as they flew on to the screen. So CNN and MSNBC followed suit, paring down the differences between the channels. MSNBC’s Lester Holt, for example, now fronts a show about the War on Terror called The Showdown Lowdown, during which he runs through the day’s Iraqrelated headlines to the accompaniment of military-techno dance music.

Isaacson also had to battle against dwindling morale at CNN. The channel thrived in its early years as the underdog with all to prove. Then it was taken over by Time Warner, and there were job cuts. On Isaacson’s watch, Time Warner merged with America Online, a marriage which ended in another 400 jobs cut at CNN.

At the same time, Isaacson and his masters at AOL Time Warner were handing down strange diktats to staff, urging on-screen talent to “smile more”. Maybe it was this kind of culture that made Isaacson decide to call it a day. His new post as head of an intellectual think-tank, the Aspen Institute, shows that he is more at home with writers and thinkers than with those obsessed with graphics that go swoosh and a whiter smile.

Jim Walton, a CNN veteran who has worked at the company since it was created by Ted Turner in 1981, has filled Isaacson’s shoes and must decide if the channel’s future lies down Ailes’s path or not.

He could reason that CNN actually has a far greater audience than Fox if you include CNN headline news and the global services, and that it should continue to act like a grown-up news organisation. After all, it is still profitable and still manages to command higher advertising rates than Fox. But the departure of Isaacson seems to indicate that those in charge of CNN’s purse-strings at AOL Time Warner, itself struggling after the resignation of its chairman, Steve Case, do not think that such a strategy is viable.