What kind of a public debate can we have on the most vital issues of the day in the United States? A lot depends on the media, which determines how these issues are framed for most people.

Take the war in Afghanistan, which has been subject to major debate here lately, as Barack Obama has to decide whether to take the advice of his commanding officer in Afghanistan, General Stanley McChrystal, and send tens of thousands more troops there, or heed public opinion, which actually favours an end to the war.

This month, one of America's most important and most-watched TV news programmes, NBC's Meet the Press, took up the issue. The lineup:

Retired General Barry McCaffrey, former army general and drug tsar (under Bill Clinton) turned defence industry lobbyist. In a news article on McCaffrey titled "One man's military-industrial-media complex", the New York Times reported that McCaffrey had "earned at least $500,000 from his work for Veritas Capital, a private equity firm in New York that has grown into a defence industry powerhouse by buying contractors whose profits soared from the wars in Afghanistan and Iraq." McCaffrey has appeared on NBC more than 1000 times since 11 September 2001.

Retired General Richard Myers, former chairman of the joint chiefs of staff under George Bush (2002-2005). He is currently on the board of directors of Northrop Grumman Corporation, one of the largest military contractors in the world, and also of United Technologies Corporation, another large military contractor.

Senator Lindsey Graham, Republican from South Carolina, a pro-war spokesperson that is one of the most regular guests on the Sunday talkshows.

Senator Carl Levin of Michigan, a Democrat, was apparently intended to represent the "other side" of the debate. Here is what he said: "Clearly we should keep the number of forces that we have. No one's talking about removing forces."

"No one" in the above sentence refers to the American people, whom Levin understandably sees as nobody in the eyes of the US media and political leaders. According to the latest New York Times/CBS News poll, 32% of those polled wanted US troops out of Afghanistan within one year or right now. That was the largest group. Another 24% wants the troops "removed within one to two years". For comparison, the leadership of the Taliban is willing to grant foreign troops 18 months to get out of their country.

In other words, a majority of 56% of Americans wants US troops out of Afghanistan about as soon as is practically feasible or even sooner. Yet Meet the Press – a mainstream network news talkshow since 1947 – does not see fit to find one person to represent that point of view. The other major TV and radio talkshows that the right also labels "liberal" in the US make similar choices almost every day.

When asked whether the US should set a timeline for withdrawal, Levin answered "no".

I know, if you have enough time you can still find an anti-war, public-interest viewpoint and the facts to support it – on the internet and even among some of the news stories in major media publications. But most Americans have other full-time jobs.

If the media's influence stopped there, the damage would be limited. After all, Americans can often still overcome the tutelage of the media's opinion leaders, as the above poll demonstrates. But the media also defines the debate for politicians. And that is where the life-and-death consequences really kick in.

If you want to know why Obama has not fought for a public option for healthcare reform, why he has caved to Wall Street on financial reform, why he has been Awol on the most important labour law reform legislation in 75 years (despite his campaign promises), just look at the major media. Think for a moment of how they would treat him if he did what his voters wanted him to do. You can be sure that Obama has thought it through very carefully.

Obama's whole political persona is based on media strategy, and on not taking any risk that the major media would turn against him. That is how he got where he is today and how he hopes to be re-elected. Many analysts confuse this with a strategy based on public opinion polling. But as we can see, these are often two different things.

Seventy-five percent of Americans support a public option for healthcare reform. (A majority would support expanding Medicare to cover everyone, but over the years the media, insurance and pharmaceutical companies made sure that this option didn't make it to the current debate.)

Obama has the bully pulpit. He could say to the rightwing Democrats in the Senate: "Look, you can vote against my proposals, but if you do not allow your president to even have a vote on this reform, you are not a Democrat." In other words, you can't join the Republicans in blocking the vote procedurally.

He could probably force Harry Reid, the Senate majority leader, to join him in enforcing this minimal party discipline that would come naturally to Republicans, which would allow the healthcare bill to pass the Senate even if conservative Democrats voted against it.

But to do that would risk losing some of Obama's post-partisan, non-ideological aura that guarantees his media support. Of course, the media is not the only influence that hobbles healthcare reform. The insurance, pharmaceutical and other business lobbies obviously have more representation in Congress than does the majority of the electorate. But Obama does not feel this direct corporate pressure nearly as much. After all, he was the first president in recent decades to get 48% of his campaign contributions from donations of less than $200 – a very significant change in American politics, made possible though internet organising.

There are other powerful elite groupings, such as the foreign policy establishment – which is more ideologically driven, like the medieval church, than a collection of lobbying interests – that thwart reform on issues of war and peace. But the major media remain one of the biggest challenges to progressive reform in the 21st century.