Glenn Greenwald and Laura Poitras will be visiting the United States to accept the Polk awards:

Glenn Greenwald and Laura Poitras, two American journalists who have been at the forefront of reporting on documents leaked by former National Security Agency contractor Edward Snowden, will return to the United States on Friday for the first time since revelations of worldwide surveillance broke.

Greenwald and Poitras, currently in Berlin, will attend Friday’s Polk Awards ceremony in New York City. The two journalists are sharing the prestigious journalism award with The Guardian’s Ewen MacAskill and with Barton Gellman, who has led The Washington Post’s reporting on the NSA documents. Greenwald and Poitras interviewed Snowden last June in Hong Kong as he first revealed himself.

In an interview with The Huffington Post, Greenwald said he’s motivated to return because “certain factions in the U.S. government have deliberately intensified the threatening climate for journalists.”

“It’s just the principle that I shouldn’t allow those tactics to stop me from returning to my own country,” Greenwald said.
Greenwald suggested government officials and members of Congress have used the language of criminalization as a tactic to chill investigative journalism.
In January, Director of National Intelligence James Clapper suggested that journalists reporting on the NSA documents were acting as Snowden’s “accomplices.” The following month, Rep. Mike Rogers (R-Mich.), chairman of the House Intelligence Committee, claimed that Greenwald was selling stolen goods by reporting stories on the NSA documents with news organizations around the world. Rep. Peter King (R-N.Y.) has called for Greenwald to be prosecuted.

Greenwald said the government has not informed his legal counsel whether or not he could face any potential charges, or if he’s been named in any grand jury investigation tied to the NSA disclosures.

My guess is that they will have to drive to the US, because they are both on the no-fly list, and I would expect all sorts of bureaucratic and law enforcement harassment.

I would place the chance of an arrest on the basis of the Espionage Act, or something similar to be about 25%.