Sen. Jeff Merkley is an unlikely choice for people's champ.

For five terms in the Oregon Legislature, Merkley was a competent but dull state representative who helped the Democratic Party gain back majorities and then served as House speaker. When he unseated then-U.S. Sen. Gordon Smith (R-Ore.) in 2008, he wasn't even the preferred candidate of Portland progressives. (They backed the insurgent Steve Novick.)

But Merkley's endorsement of Sen. Bernie Sanders (I-Vt.) for president in 2016 earned him some cred within the party's left wing. And since the election of President Donald Trump, Merkley has circled the White House like an angry horsefly.

Last November, he called Steve Bannon and other Trump advisers "white supremacists" before that epithet was commonplace. In February, he aided Sen. Elizabeth Warren (D-Mass.) in reading into the Congressional Record Coretta Scott King's letter describing the racial intimidation of black voters by Attorney General Jeff Sessions. And last month, he spoke for more than 15 hours in an unsuccessful bid to block Neil Gorsuch's appointment to the U.S. Supreme Court.

In a conversation with WW on May 12, he laid out his current thinking on our president and the fate of the nation.

WW: What's keeping you up at night?

Sen. Jeff Merkley: We're staring into the abyss. We're on the edge of a constitutional crisis. The president has fired the person who is driving the only aggressive investigation into the conduct of the Trump campaign and the possibility of coordination or collusion with the Russians, and that's unacceptable. If we're going to have justice for all, and if no one's above the law, then you can't have a president crushing an investigation into his team.

What do you say to people who haven't looked very closely at the details and say this is just more partisan political theater?

Step into the shoes on the other side of the political equation. Ask yourself, how would you feel if a Democratic president derailed an investigation into the Democratic presidential team? That allows people to all be Americans in this. We are not Democrats and Republicans. This is a fight for the integrity of the foundation of our democratic republic. Elections are incredibly important to our "We the People" republic. A foreign power deliberately interfered in those elections. Russian interference occurred on a massive scale, and if any American cooperated, colluded or coordinated, it's not just a crime against the Constitution. This is the worst sort of treason. That would be treasonous conduct, and we have to get to the bottom of it.

At this point, do you believe that treason occurred?

I think there is a very good chance, better than even odds, that it has occurred, yes.

Let's imagine for a moment that Trump advisers Paul Manafort and Roger Stone colluded with Russian officials. If Donald Trump was not personally involved in this, what significance does it have for the public?

It means that the integrity of the election was violated, and it certainly decreases the legitimacy of this presidency even if Trump personally was not involved. The president is clearly extremely worried about an investigation. For him to take this action—to decide he's going to derail the investigation—it shows how obsessed the president is about the possibility of an investigation uncovering information that would affect his presidency.

Are you ready to call for impeachment proceedings at this point?

I'm not ready to call for impeachment at this moment. I am ready to say we must have a special prosecutor in place, chosen by the top career member of the Justice Department.

What I hope happens in the next few days is that the Senate Republicans join us to fully question the attorney general, the deputy attorney general, and the former FBI director, [James] Comey. I hope that following that we can have an executive session of the Senate. The point of that is, without any cameras, without any press, we can have an honest conversation with each other about how important this is to the integrity of our government.

All my effort at this point is directed toward, let's get all the facts. 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.

Whoever conducts an investigation will be relying on facts gathered by the FBI. How comfortable are you trusting them?

I don't believe they necessarily have to go straight through the FBI. We know a lot about what the Russians did. We know that they created a false news operation. We know that they created an organization with a thousand people who were basically pretending to be Americans and weighing in on social media. We know that they amplified the impact of social media by using a botnet around the world to have robots that were responding and putting out comments to again amplify the effect and try to get stories onto the Facebook screen of Americans. We know that they hacked computers, we know that they released information from those hacks on a very timely basis to influence the campaign. And we know that there were a lot of conversations between members of the Trump team and the Russians.

But we need to know if those conversations were tied in any way to this set of activities I have just described. If they were simply saying, for example, "What are the issues important to Russia, and how do we build a better relationship between our two nations?" there's nothing wrong with that. But if there were conversations about the campaign and how to gain additional assistance in derailing Hillary Clinton's team and her campaign, then that's treasonous conduct. So that's what we have to find out. A special prosecutor should have the powers, the team, the resources, the experience, the professionals to be able to get to the bottom of this.

Putting aside the knowns and the unknowns of the Russia investigation, is the president of sound mind?

[Long pause] I am deeply disturbed by many of the actions he has taken and the manner he's taken them in. I'll leave it to psychologists to say if he's of sound mind, but he often appears not to be on a stable foundation.

Some say the future of the country depends on eight or so Republican senators who have demonstrated some independence from the president: John McCain and Jeff Flake in Arizona, or Lindsey Graham in South Carolina. How much faith do you have in them?

I believe there is a very good chance that [my] Republican colleagues are going to step forward—not to say that we have the hard facts and the president should resign, but to say there are enough disturbing known facts that a full, aggressive investigation is necessary for the integrity of our government.

This all seems very far away and out of our control. What can Oregonians do?

Oregonians need to remind their legislators how incredibly important this is to the integrity of our government. Not only is it relevant to the pursuit of justice, but it is very relevant to whether we continue to have faith in our system to deliver government of, by and for the people.

Have you spoken with Rep. Greg Walden about his role in dismantling the Affordable Care Act?

I have not talked to him about it.

What would you say to him?

I would tell him about my town halls that I've had in his district where so many of his constituents are coming out in a pure panic over the Trumpcare bill that came out of the House. You have a lot of lower-income folks living in rural Oregon who before Obamacare were deeply stressed that if a loved one got sick, they would not get the care that they need and that they might end up going bankrupt trying to get the care they need. One out of three individuals in his district is on the Oregon Health Plan. Of course, he knows this, and I know that he knows this.

So this country is divided, fracturing and often disengaged. What reason is there for optimism?

I don't think people are tuning out. At least what I see is the enormous energy of people tuning in, people who got complacent. Many things were in a better place, but that bred complacency that gave us Donald Trump. I see people highly, highly mobilized. The turnouts in my town halls are massive whether I'm in Democratic counties or Republican counties. So that's a starting point.