U.S. Senator Jeff Merkley (D-Ore.) got his wish: a special counsel investigating President Donald Trump.

This afternoon, Deputy U.S. Attorney General Rod Rosenstein announced he will appoint former FBI Director Robert Mueller as a special counsel to investigate whether Trump or his aides collaborated with the Russian government during the 2016 presidential campaign.

Merkley was triumphant.

"This is a victory for all Americans who believe in the integrity of the rule of law," he said in a statement. "This investigation must be given the full resources and independence it needs to succeed. We must follow the facts wherever they lead, and demand complete accountability for any wrongdoing that is found."

Sen. Ron Wyden (D-Ore.) was more succinct in his statement: "This is a start at figuring out what exactly happened to our democracy."

In an interview with WW in this week's print edition, Merkley laid out the case for a special prosecutor or special counsel.

“All my effort at this point is directed toward, let’s get all the facts,” Merkley told WW. “If we find that members of the president’s team were in any way operating, with the knowledge of or at the request of the president, to coordinate or to amplify any of the Russian activity in the campaign, then that is 100 percent clear impeachable activity. And I will be calling for a fast and sure process in the House to conduct impeachment at that point.”

Related: Read full interviews with Merkley and Wyden here.