President Obama has decided to pursue a dangerous strategy that could cause irreparable harm to freedom of the press as we know it. According to Charlie Savage of the New York Times, Attorney General Eric Holder is investigating the possibility of prosecuting WikiLeaks founder Julian Assange in connection with the 250,000 diplomatic cables stolen – according to the government – by army private Bradley Manning.

By longstanding first amendment tradition, third parties such as news organisations — even an unconventional one like WikiLeaks — are not prosecuted for publishing leaked material, even if the person who gave it to them broke the law. So, Holder is working on the theory that WikiLeaks "colluded" with Manning, acting not as a passive recipient, but as an active participant in persuading Manning to give up the goods.

The problem is that there is no meaningful distinction to be made. How did the Guardian, equally, not "collude" with WikiLeaks in obtaining the cables? How did the New York Times not "collude" with the Guardian when the Guardian gave the Times a copy following Assange's decision to cut the Times out of the latest document dump?

For that matter, I don't see how any news organisation can be said not to have colluded with a source when it receives leaked documents. Didn't the Times collude with Daniel Ellsberg when it received the Pentagon Papers from him? Yes, there are differences. Ellsberg had finished making copies long before he began working with the Times, whereas Assange may have goaded Manning. But does that really matter?

What matters is whether publishing leaked documents poses such a grave danger to national security that it warrants prosecution. The supreme court, in the 1931 case of Near v Minnesota, ruled that the standard for stopping publication – that is, for censorship – is whether the information is so sensitive that it would be akin to revealing the movement of troops during wartime. That standard was affirmed in the 1971 Pentagon Papers case, New York Times Company v United States, in which the Court ruled the Nixon administration could not censor the Times and the Washington Post.

What's less clear is whether news organisations can be prosecuted after publication under something easier to prove than the troops-in-time-of-war standard. As my friend and occasional collaborator Harvey Silverglate has pointed out, the Nixon White House took some steps to bring criminal charges against the Times and the Post after the Pentagon Papers were published, but dropped the matter after the then president became overwhelmed by the Watergate scandal.

More recently, Silverglate notes, there were calls on the right to prosecute the Times and the Post under the Espionage Act of 1917 after their 2005 exposure of the Bush administration's secret wiretapping program (the Times) and the CIA's secret prisons in eastern Europe (the Post). Then President Bush, to his credit, did nothing of the kind, despite referring to the Times' exposé as "a shameful act".

The Obama-Holder wrinkle is to attempt to draw distinctions between WikiLeaks and the traditional media. It can't be done. The rhetoric of Assange and his supporters can sometimes be a little scary. In fact, though, their actions have been quite moderate. The US state department cables, after all, were not top secret, and WikiLeaks says it has taken pains to withhold potentially dangerous information.

In that respect, attempts to separate the Times and the Guardian, on the one hand, and WikiLeaks, on the other, should be seen as entirely political. Presumably, dragging a handcuffed-and-shackled Assange into federal court would prove quite popular. By contrast, sentencing Times publisher Arthur Sulzberger to a long stint in a federal penitentiary would likely prove too much, even though senator Joe Lieberman, an occasionally moderate former Democrat, has suggested that the Times could be prosecuted.

Almost since his inauguration nearly two years ago, Barack Obama has been disappointing liberals, whether it's through his half-measures on the economy and healthcare, his continued pursuit of unpopular wars in Iraq and Afghanistan or his failure to close Guantánamo, the very symbol of Bush-era overreach. Some of those complaints are overwrought. Politics is the art of the possible, and Obama can justifiably claim to have done what's possible in the face of Republican intransigence and the sheer difficulties of what he has faced.

By contrast, the White House's legal war against WikiLeaks is a shameful assault on our guarantee of free speech and a free press. It's ironic that after two years of bogus claims from the right that Obama is dismantling the constitution, now that he really is, the only people who seem to care are on the left.