For most of American history, it was rare for the government to treat the leaking of its secrets to the news media as a crime. But starting in the second half of the George W. Bush administration and accelerating during the Obama administration, the Justice Department began making much more routine use of the Espionage Act to go after officials who provided information to the public through reporters, as opposed to actual spies. The World War I-era law criminalizes the disclosure of potentially damaging national security secrets to someone not authorized to receive them.

On its face, the Espionage Act could also be used to prosecute reporters who publish government secrets. But many legal scholars believe that prosecuting people for acts related to receiving and publishing information would violate the First Amendment.

That notion has never been tested in court, however, because until now the government has never brought such charges. The closest it came was indicting two lobbyists for a pro-Israel group in 2005 who received classified information about American policy toward Iran and passed it on. But that case fell apart after several skeptical pretrial rulings by a judge, and the charges were dropped.

Though he is not a conventional journalist, much of what Mr. Assange does at WikiLeaks is difficult to distinguish in a legally meaningful way from what traditional news organizations like The Times do: seek and publish information that officials want to be secret, including classified national security matters, and take steps to protect the confidentiality of sources.

The Obama administration had also weighed charging Mr. Assange, but rejected that step out of fears that it would chill investigative journalism and could be struck down as unconstitutional. A Justice Department official declined to address whether there was any new evidence that had come to light recently or whether the Trump administration had simply decided to take a step the Obama administration had shied away from.

The three charges that squarely addressed Mr. Assange’s publication of government secrets were focused on a handful of files that contained the names of people who had provided information to the United States in dangerous places like the Afghanistan and Iraq war zones, and authoritarian states like China, Iran and Syria.

The evidence laid out in the indictment against Mr. Assange mapped onto information presented by military prosecutors in the 2013 court-martial trial of Ms. Manning. Prosecutors in her case also alleged that her actions endangered the people whose names were revealed in the documents when Mr. Assange published them, though they presented no evidence that anyone was killed as a result.