President Donald Trump says a special prosecutor for an investigation into Russia’s involvement in the election hurts our country.

He called the probe a “witch hunt” and “totally ridiculous” Thursday afternoon. At a news conference, Trump said, “I respect the move but the entire thing is a witch hunt. There is no collusion between certainly myself and my campaign. But I can always speak for myself and the Russians, zero.”

Former FBI Director Robert Mueller will be the special prosecutor overseeing the investigation. The move has received praise from both Republicans and Democrats.

Thursday afternoon, Deputy Attorney General Rod Rosenstein, the man who appointed Mueller, briefed senators behind closed doors. Both Senators Amy Klobuchar and Al Franken attended the highly unusual closed-door briefing by Rosenstein.

Senator Klobuchar said stakes could not be higher.

When President Trump tweeted this morning, “This is the single greatest witch hunt of a politician in American history,” Senator Amy Klobuchar quickly responded tweeting, “This is a truth hunt.”

“We have been so proud for centuries here to have free elections, fair elections, not influenced by foreign countries, not influenced by foreign powers, what this is really about is protecting that democracy,” Klobuchar said.

Klobuchar praised the selection of Robert Mueller, who was first appointed FBI director by President George W. Bush.

“I think it’s much better to have someone who served a Republican president and a Democratic president, George Bush and Barack Obama as the FBI Director, so well respected look into this,” Klobuchar said.

Other Minnesota Democrats took to social media, also praising the appointment, as did Minnesota Republican Congressmen Erik Paulsen and Jason Lewis.

Constitutional law Professor David Schultz says the Mueller investigation, like other special prosecutor investigations in U.S. History, will likely take months, even years, and will affect the President’s ability to push for key agenda items.

“I think for months, well into 2018, we are going to see this administration hobbled by this investigation.” Jacobs said.

One big historical difference in terms of the appointment of this special prosecutor is that it is coming so early in the Trump presidency. In the cases of Presidents Nixon, Reagan and Clinton, special prosecutors were conducting investigations that took place years into their presidencies.