The arrest of WikiLeaks founder Julian Assange has prompted a round of calls that the document-leaker be prosecuted by U.S. authorities for espionage.

That idea, which is about the only one in recent memory that has attracted bipartisan support in Washington, is ill-conceived and fraught with problems — based on the evidence now available.

It’s understandable that the powers- that-be in Washington are incensed by the role Assange has played in divulging what are supposed to be secret, internal government communications for all the world to see.

Last week, five news organizations began publishing stories based on some 250,000 confidential diplomatic cables that Assange had gotten his hands on. Exactly how Assange came to acquire them is yet to be established, but an Army private involved in intelligence matters for the U.S. has been implicated in downloading them from secure computers.

U.S. Army Pfc. Bradley Manning is being held in solitary confinement at Quantico, Va. If the allegations against him are true, he ought to be prosecuted vigorously.

However, carrying that prosecution outward to Assange, the disseminator of the information, is far less certain territory. For one thing, the Espionage Act, a 1917 law, has never been used to prosecute the recipient of information important to national security.

For another, the success of the case could turn on whether WikiLeaks is defined as a media outlet. It’s possible, given the evolving and increasingly digital nature of journalism.

It would be ironic if a statute that dates from 1917, written in an era of paper documents, were the vehicle to define what constitutes a media outlet in the age of the Internet.

Acquiring and publishing information is at the heart of the definition of a free press, which has substantial First Amendment protections.

Treading on these, even in a case with an antagonist as undeserving of sympathy as Assange, could set dangerous precedents in criminally pursuing all manner of media outlets.

Nevertheless, there are calls from politicians for just such action.

Sen. Dianne Feinstein, a Democrat and chair of the Senate Intelligence Committee, wrote an op-ed piece published in The Wall Street Journal this week advocating prosecution of Assange for espionage. Mitch McConnell, Republican leader in the Senate, called Assange a “high-tech terrorist” who “needs to be prosecuted to the full extent of the law.”

Meanwhile, Assange sits in jail in London awaiting the resolution of charges that he sexually assaulted two women in Sweden, allegations that on their face are unrelated to the WikiLeaks situation. Some hint darkly that the charges are a ruse, an effort to get Assange transported to Sweden, which has a strong extradition treaty with the U.S.

We surely hope not. Instead of prosecuting Assange, the U.S. government ought to focus on better securing information that it deems important to national security.