Since the nineteen-seventies, Gallup has been polling Americans annually about their confidence in their country’s institutions—the military, the Supreme Court, Congress, the Presidency, organized religion, the health-care establishment, and public schools, among others. Over all, the project describes a collapse in trust over time, even though the surveys started amid the disillusionment of Watergate and the failed war in Vietnam. In 1973, more than four in ten Americans had “a great deal” or “quite a lot” of confidence in Congress. This year, the figure was twelve per cent. Trust in churches and other religious institutions has fallen from sixty-five per cent to forty-one per cent in the same period. Confidence in public schools has dropped from fifty-eight per cent to thirty-six per cent. The loss of faith in the “medical system” has been particularly dramatic—a decline from eighty per cent in 1975 to thirty-seven per cent this year. There are a few exceptions to the broad slide. Confidence in the police has held steady at just above fifty per cent. Confidence in the military has increased, from fifty-eight per cent in the aftermath of the Vietnam War to seventy-two percent this year. Otherwise, it isn’t clear where citizens have redirected their faith, or whether they have at all.

The polarization and tribalization in today’s politics may exacerbate this loss of confidence or contribute to it, or both. Increasingly, daily life is mediated less by the institutional doors we walk through from day to day and more by the connections and decisions we make online. Last week, Tim Wu, the law professor and author, wrote in the Times that, for example, the boom in bitcoin—a virtual currency whose market price had, he noted, risen from thirty-nine cents apiece to more than eighteen thousand dollars in just eight years—reflects how, “More and more, we are losing faith in humans and depending instead on machines.” The danger, though, extends beyond financial bubbles.

Even in a stable constitutional republic, a cynical or unmoored citizenry presents an opportunity for demagogues and populists. As much as stagnant wages in former manufacturing regions, glaring economic inequality, or white backlash after the Obama Presidency, the country’s disillusionment with institutions enabled Donald Trump’s election. Trump had a sound instinct as he took office that public disgust with élites, including those running the Republican Party, ran so deep that he—even as a New York billionaire—could get away with outrageous attacks on people or agencies previously believed to be off limits for a President, because of the political backlash that the attacks would generate. After his Inauguration, for example, Trump did not hesitate to denigrate the C.I.A. and other intelligence agencies for promoting their independent judgment that Russia had sought to aid his campaign. And the President’s opportunistic assaults on less popular institutions—such as the news media and Congress—have riled his base.

All this suggests the need for a certain realism and vigilance about the rising volume of attacks by Trump and his allies on Robert Mueller, the special counsel leading the investigation into possible Russian interference in the election and (increasingly) related issues, and on the F.B.I., whose agents carry out much of the investigative work. Presidents Nixon, Reagan, and Clinton all denigrated the counsels who investigated them. Nixon went so far as to fire some of those he saw as his tormentors, in the infamous Saturday Night Massacre. Judging by the indictments of certain Trump associates, such as his former campaign chairman Paul Manafort, and the coöperation agreements by others, notably Michael Flynn, his former national-security adviser, it is conceivable that during the next year Trump will face a choice between radical action—issuing preëmptive pardons, firing Mueller or the Deputy Attorney General Rod Rosenstein—and allowing someone close to him, perhaps even a family member, to face criminal charges. It is hard to imagine him reacting to that dilemma with care or caution.

On Wednesday, Senator Mark Warner, the ranking Democrat on the Senate Intelligence Committee, apparently alarmed by the attacks on Mueller, delivered a warning in a speech on the Senate floor. “Any attempt by this President to remove Special Counsel Mueller from his position or to pardon key witnesses in any effort to shield them from accountability or shut down the investigation would be a gross abuse of power and a flagrant violation of executive-branch responsibilities and authorities,” Warner said. “These truly are red lines, and we simply cannot allow them to be crossed.” The White House attorney Ty Cobb responded that “no consideration” was being given to firing Mueller, but, given Trump’s record of saying one thing and doing another, and of overruling his spokespeople, it was hardly a persuasive denial.

Warner said he hoped that senators and members of Congress from both parties would speak out similarly, to make clear that his position represented an institutional consensus, not a partisan attack. That seems unlikely. Many establishment Republican leaders might be pleased if the facts uncovered by Mueller so damaged Trump that it weakened his grip on the Party and discredited his nativist, America First movement. But, if a significant number of Republicans challenge Trump in public during the 2018 midterm cycle to defend the prerogatives of Congress or the F.B.I., they would be showing a kind of courage that few members have offered since Trump won their party’s nomination, in 2016.

It is tempting to think that an institution like the F.B.I. enjoys such credibility and public support that its agents and officials—and Mueller himself—can rely on cross-party backing in a crisis, even if Republicans remain silent now. Perhaps. But this was a party that refused to challenge Trump’s backing of Roy Moore in Alabama’s Senate race. And an understanding of what core Trump supporters believe about the F.B.I. and Mueller has to take into account Gallup’s trend lines. While celebrating this new year, it will require a certain degree of evidence-light optimism to be convinced that the center will hold.