When a former president of the United States weighs in on an ongoing criminal investigation, there is considerable risk that his comments could make it impossible for justice to be fair and objective.

Recently, former President George W. Bush said that Julian Assange, the founder of WikiLeaks, "has willfully and repeatedly done great harm to the interests of the United States." He made this statement, through a spokesman, in explaining why he was canceling a speech he had agreed to deliver to the Young Presidents Organization. He said he "had no desire to share a forum with" Assange, even though Assange was to speak by videoconference and they would not literally be sharing a platform or forum.

President Bush is, of course, not alone in expressing negative views about Assange and WikiLeaks, and all Americans have the freedom to express their personal opinions on the leaking of diplomatic cables. Many have argued that the WikiLeaks has actually done great good both for democracy in general and for the United States in particular. That is a healthy debate that will continue to play out around the world, especially in the context of recent developments in the Middle East.

But when a former President states, categorically, that Assange has "willfully and repeatedly done great harm" to our country, such a statement has the potential to distort the processes of justice.

First, former presidents are aware of classified material not generally available to other participants in the marketplace of ideas. His "harm assessment," therefore is likely to carry more weight than other opinions expressed about the effects of WikiLeaks on our national interest. It is as if the former president had said, "Trust me. I know. I've seen things you can't see. There really has been 'great harm.'" Those of us who have litigated national security cases, such as the ones that grew out of the publication of the Pentagon Papers, know that governmental claims of "great harm" are often overstated and prove in the end to be unfounded, but potential jurors may not have the experience necessary to assess such overblown claims. They are likely to assume that if a former president has said there was "great harm," he must know what he was talking about, because he had daily access to the most highly classified intelligence reports.

Even though we are a long way from any possible jury trial -- if one were ever to occur -- the kind of statement made by former President Bush becomes part of the atmospherics and its impact can never be fully known or quantified. That is why former presidents generally decline to offer comments about the possible subjects of ongoing criminal investigations.

The Bush statement could have a more immediate impact on investigative and prosecutorial decisions. The members of the grand jury secretly hearing evidence in the northern district of Virginia -- deliberately selected by prosecutors because of the high density of military intelligence and government families in the area -- could be prejudiced by the former president's assessment of the harms allegedly caused by the leaks, especially since grand jurors hear only the government's side of the case. And the military investigators who have just issued enhanced charges against Pfc. Bradley Manning -- including "aiding the enemy" -- may well have been influenced by their former Commander in Chief. Moreover, by declaring that Assange has caused "great harm" to our nation, the former president -- a Republican -- has thrown down a political gauntlet.

Can a Democratic president and attorney general now be perceived as less protective of our national interests than a Republican president? Bush's statement threatens to politicize the ongoing investigations and prosecutorial decision by putting pressure on the current administration to be tough on Assange because of the "great harm" Bush says he caused.

Finally, the language, tone and context of the Bush statement threatens to make Assange into a Pariah -- a dehumanized enemy undeserving of a hearing or a fair trial -- in the eyes of those who admire the former president. Bush not only criticized Assange, he refused to associate with him, even at a distance. This "boycott" of Assange tends to lend credence to the far more extreme mischaracterizations and threats leveled against Assange by assorted politicians who have accused him of "treason" and demanded his execution and even his assassination.

There are strong constitutional, legal and policy reasons why Julian Assange should not be the subject of any criminal investigation or prosecution. These reasons relate not only to the rights of Assange and WikiLeaks, but as well to the First and Fourth Amendment right of American citizens who follow WikiLeaks and read the materials they have brought into the marketplace of ideas.

The danger is that if and when these arguments need to be presented in a legal context, those who must make the important decisions -- prosecutors, investigators, judges, jurors, political figures and ultimately the general public -- may be prejudiced by the kinds of gratuitous statements made by former President George W. Bush and other past and current political figures. That simply is not fair or just.

Alan M. Dershowitz is a legal consultant to Julian Assange's British defense team.

