Glenn Greenwald said during a Sunday appearance on ABC News' "This Week" that even "low-level" National Security Agency analysts have access to a "powerful and invasive" tool that allows them to spy on the private emails and phone calls of Americans.

“The NSA has trillions of telephone calls and emails in their databases that they’ve collected over the last several years,” Greenwald told George Stephanopoulos. “And what these programs are, are very simple screens, like the ones that supermarket clerks or shipping and receiving clerks use, where all an analyst has to do is enter an email address or an IP address, and it does two things. It searches that database and lets them listen to the calls or read the emails of everything that the NSA has stored, or look at the browsing histories or Google search terms that you’ve entered, and it also alerts them to any further activity that people connected to that email address or that IP address do in the future.”

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“There are legal constraints for how you can spy on Americans,” Greenwald said. “You can’t target them without going to the FISA court. But these systems allow analysts to listen to whatever emails they want, whatever telephone calls, browsing histories, Microsoft Word documents.”

“And it’s all done with no need to go to a court, with no need to even get supervisor approval on the part of the analyst,” he added.