House Intelligence Committee Chairman Adam B. Schiff (D-Calif.) speaks on Capitol Hill on Feb. 6. (J. Scott Applewhite/AP)

Adam B. Schiff, a Democrat, represents California’s 28th Congressional District in the House and is chairman of the Intelligence Committee.

This is a moment of great peril for our democracy. Our country is deeply divided. Our national discourse has become coarse, indeed, poisonous. Disunity and dysfunction have paralyzed Congress.

And while our attention is focused inward, the world spins on, new authoritarian regimes are born, old rivals spread their pernicious ideologies, and the space for freedom-loving peoples begins to contract violently. At last week’s Munich Security Conference, the prevailing sentiment among our closest allies is that the United States can no longer be counted on to champion liberal democracy or defend the world order we built.

For the past two years, we have examined Russia’s interference in the 2016 election and its attempts to influence the 2018 midterms. Moscow’s effort to undermine our democracy was spectacularly successful in inflaming racial, ethnic and other divides in our society and turning American against American.

But the attack on our democracy had its limits. Russian President Vladimir Putin could not lead us to distrust our own intelligence agencies or the FBI. He could not cause us to view our own free press as an enemy of the people. He could not undermine the independence of the Justice Department or denigrate judges. Only we could do that to ourselves. Although many forces have contributed to the decline in public confidence in our institutions, one force stands out as an accelerant, like gas on a fire. And try as some of us might to avoid invoking the arsonist’s name, we must say it.

I speak, of course, of our president, Donald Trump.

The president has just declared a national emergency to subvert the will of Congress and appropriate billions of dollars for a border wall that Congress has explicitly refused to fund. Whether you support the border wall or oppose it, you should be deeply troubled by the president’s intent to obtain it through a plainly unconstitutional abuse of power.

To my Republican colleagues: When the president attacked the independence of the Justice Department by intervening in a case in which he is implicated, you did not speak out. When he attacked the press as the enemy of the people, you again were silent. When he targeted the judiciary, labeling judges and decisions he didn’t like as illegitimate, we heard not a word. And now he comes for Congress, the first branch of government, seeking to strip it of its greatest power, that of the purse.

Many of you have acknowledged your deep misgivings about the president in quiet conversations over the past two years. You have bemoaned his lack of decency, character and integrity. You have deplored his fundamental inability to tell the truth. But for reasons that are all too easy to comprehend, you have chosen to keep your misgivings and your rising alarm private.

That must end. The time for silent disagreement is over. You must speak out.

This will require courage. The president is popular among your base, which revels in his vindictive and personal attacks on members of his own party, even giants such as the late senator John McCain. Speaking up risks a primary challenge or accusations of disloyalty. But such acts of independence are the most profound demonstrations of loyalty to country.

Special counsel Robert S. Mueller III may soon conclude his investigation and report. Depending on what is in that report and what we find in our own investigations, our nation may face an even greater challenge. While I am alarmed at what we have already seen and found of the president’s conduct and that of his campaign, I continue to reserve judgment about what consequences should flow from our eventual findings. I ask you to do the same.

If we cannot rise to the defense of our democracy now, in the face of a plainly unconstitutional aggrandizement of presidential power, what hope can we have that we will do so with the far greater decisions that could be yet to come?

Although these times pose unprecedented challenges, we have been through worse. The divisions during the Vietnam War and the civil rights movement were just as grave and far more deadly. The Depression and World War II were far more consequential. And nothing can compare to the searing experience of the Civil War.

If Abraham Lincoln, the father of the Republican Party, could be hopeful that our bonds of affection would be strained but not broken by a war that pitted brother against brother, surely America can come together once more. But as long as we must endure the present trial, history compels us to speak, and act, our conscience, Republicans and Democrats alike.