For all their messy infighting, Americans long have been bound together by their belief in a set of principles and institutions larger and more enduring than any single person. From its founding, this nation chose to be governed by the rule of law as a way to constrain the actions and decisions of any individual leader. And when it counts, Americans have come together as a unified front against common enemies.

That all is under threat now, and amid a growing rat’s nest of developments, the primary cause is the one that has bedeviled this nation for months: overt Russian interference in the 2016 presidential election. What the country still does not know — but must determine — is the extent of that interference, who was involved and who benefited.

President Trump has not helped matters. Despite numerous personal, family and associate connections, he refuses to release the tax returns that might at least clarify his business dealings with Russia, a nation he once bragged of having done “a lot of business with.” Some of his closest campaign aides, including his manager, had ties to Russia. His sons still may. Trump was forced to fire National Security Adviser Michael Flynn over interactions with Russia. He later fired the acting attorney general, Sally Yates, who alerted him to Flynn’s mendacity, and now FBI director James Comey, who was leading the multifaceted Russian investigation.

On Friday, Trump’s attorneys said their review of the last 10 years of tax returns did not turn up “any income of any type from Russian sources,” with minor exceptions. But the lawyers, who did the review at Trump’s request, did not release copies of the returns.

There’s also the spectacle of Trump admitting he personally queried Comey on whether he was under investigation. Attorney General Jeff Sessions may have violated his recusal pledge to provide a pretext for firing Comey, but Trump now acknowledges he would have fired Comey no matter what. The mere fact that Trump maintains Comey assured him he was not under investigation is by itself in need of investigation.

For Comey to have told anyone — even the president — that they were not part of an active investigation would be a serious ethical breach and possibly illegal. It is implausible to think an FBI director and former deputy U.S. attorney general would do so. Adding to the suspicious sequence of events, Comey had, just days before, reportedly requested additional money and agents to expand the investigation. Instead of funding, he got fired — less than 48 hours before he was scheduled to testify. And on Friday, Trump tweeted that Comey had better hope there are no “tapes” of their conversations.

Given all of this, it is beyond disappointing that veteran figures such as Senate Judiciary Chairman Chuck Grassley and Senate Majority Leader Mitch McConnell defiantly oppose an independent inquiry. Grassley even resorted to this coarse dismissal: “Suck it up and move on.” That kind of circle-the-wagons reaction to possible obstruction of justice and collusion with an adversarial nation is unacceptable. It weakens the very institutions designed to provide a check on the misuse of power.

Russia’s intent here has been not just to influence the election, but to erode American confidence in and commitment to the democratic principles and institutions that have made this country a beacon to others. Sowing discord jeopardizes the national unity and purpose that strengthens this country against malicious outside forces.

It’s heartening that some Republicans have dared to put country first, among them Minnesota U.S. Rep. Erik Paulsen, who earlier this week stepped forward to become the first Republican in the state’s congressional delegation to call for an independent investigation.

The circumstances surrounding Comey’s firing, Paulsen said, “call for an independent investigation that the American people can trust with confidence.” That’s a message his colleagues, Reps. Jason Lewis and Tom Emmer, should echo. Doing so would not be seen as any betrayal of party, country or the office of the president, but rather a bold move to affirm the rule of law that is a democracy’s ultimate protection.