U.S. Sen. Ron Wyden, D-Ore., ranking member of the Senate Finance Committee.

The ranking Democrat of the Senate Finance Committee said Monday that a "full-fledged constitutional crisis" will unfold if President Donald Trump tries to interfere with special counsel Robert Mueller's investigation into potential coordination between Trump campaign officials and Russia during the 2016 election.

"I think every member of Congress -- every Democrat, every Republican, House and Senate -- needs to say now that if there is any effort by the president to interfere with the work of Bob Mueller, there's going to be a real constitutional crisis in America," said Sen. Ron Wyden.

The Oregon Democrat said Mueller is "making a case that runs right up to the top of the Trump administration" and that he's "pleased" with the special counsel's work. So far, Mueller has secured indictments of Trump's former campaign manager and a business partner, as well as guilty pleas for lying to FBI agents by a campaign aide and Michael Flynn, the president's former national security adviser.

Trump has denied any wrongdoing. On Monday, he cast the investigation as the "greatest Witch Hunt in U.S. political history" in a tweet.

Wyden said Mueller and his team appear to be probing questionable financial arrangements of Trump associates, which he said is "the single most important key to unlock this inquiry." Paul Manafort, Trump's former campaign manager, has been charged with money laundering, among other charges. The charges are not related to Manafort's work for the Trump campaign.

There's no evidence that Mueller's team has found a smoking gun showing collusion or direct evidence of wrongdoing by Trump. However, court records show Flynn and the other official who pleaded guilty, former Trump campaign policy adviser George Papadopoulos, agreed to be cooperating witnesses in exchange for leniency.

While Trump himself has not signaled that he will remove Mueller as special counsel or otherwise directly interfere with the investigation, the president has made statements meant to sow doubt about the impartiality of Mueller and his agents. In particular, Trump has highlighted that several of Mueller's investigators were Hillary Clinton donors and that others allegedly made disparaging remarks about Trump.

Wyden, speaking to reporters at a business summit in Portland, said that Oregonians want officials to get to the bottom of any Trump campaign links to Russia.

"Oregonians understand that this is not fake news," Wyden said.

-- Gordon R. Friedman

503-221-8209; @GordonRFriedman