Antitrust review will occur within the Justice Department and the Federal Communications Commission (FCC).
Still, Congress will get a word in, helping shape the political debate about the merger. Watt will question the CEOs of AT&T and T-Mobile's parent company, Deutsche Telekom, in a hearing on Thursday.
But that doesn't mean playing a role in whether the merger goes through, Watt emphasized.
"It's not our job to be out there to be demagoguing on one side or the other," he said.