Jeff Flake, a Republican, is a U.S. senator from Arizona.

As I contemplate the Trump presidency, I cannot help but think of Joseph Welch.

On June 9, 1954, during the Army-McCarthy hearings, Welch, who was the chief counsel for the Army, famously asked the committee chairman if he might speak on a point of personal privilege. What he said that day was so profound that it has become enshrined as a pivotal moment in defense of American values against those who would lay waste to them. Welch was the son of a small prairie town in northwest Iowa, and the plaintive quality of his flat Midwestern accent is burned into American history. After asking Sen. Joseph McCarthy for his attention and telling him to listen with both ears, Welch spoke:

"Until this moment, senator, I think I never really gauged your cruelty, or your recklessness."

And then, in words that today echo from his time to ours, Welch delivered the coup de grace: "You've done enough. Have you no sense of decency, sir, at long last? Have you left no sense of decency?"

The moral power of Welch's words ended McCarthy's rampage on American values, and effectively his career as well.

After Welch said his piece, the hearing room erupted in applause, those in attendance seemingly shocked by such bracing moral clarity in the face of a moral vandal. Someone had finally spoken up and said: Enough.

By doing so, Welch reawakened the conscience of the country. The moment was a shock to the system, a powerful dose of cure for an American democracy that was questioning its values during a time of global tumult and threat. We had temporarily forgotten who we were supposed to be.

We face just such a time now. We have again forgotten who we are supposed to be.

There is a sickness in our system — and it is contagious.

How many more disgraceful public feuds with Gold Star families can we witness in silence before we ourselves are disgraced?

How many more times will we see moral ambiguity in the face of shocking bigotry and shrug it off?

How many more childish insults do we need to see hurled at a hostile foreign power before we acknowledge the senseless danger of it?

How much more damage to our democracy and to the institutions of American liberty do we need to witness in silence before we count ourselves as complicit in that damage?

Nine months of this administration is enough for us to stop pretending that this is somehow normal, and that we are on the verge of some sort of pivot to governing, to stability. Nine months is more than enough for us to say, loudly and clearly: Enough.

The outcome of this is in our hands. We can no longer remain silent, merely observing this train wreck, passively, as if waiting for someone else to do something. The longer we wait, the greater the damage, the harsher the judgment of history.

I have been so worried about the state of our disunion that I recently wrote a book called "Conscience of a Conservative: A Rejection of Destructive Politics and a Return to Principle." I meant for the book to be a defense of principle at a time when principle is in a state of collapse. In it, I traced the transformation of my party from a party of ideas to a party in thrall to a charismatic figure peddling empty populist slogans. I tried to make the case for the sometimes excruciating work of arguing and compromise.

This was part of the reason I wanted to go to the Senate — because its institutional strictures require you to cross the aisle and do what is best for the country. Because what is best for the country is for neither party's base to fully get what it wants but rather for the factions that make up our parties to be compelled to talk until we have a policy solution to our problems. To listen to the rhetoric of the extremes of both parties, one could be forgiven for believing that we are each other's enemies, that we are at war with ourselves.

But more is now required of us than to put down our thoughts in writing. As our political culture seems every day to plumb new depths of indecency, we must stand up and speak out. Especially those of us who hold elective office.

To that end, and to remove all considerations of what is normally considered to be safe politically, I have decided that my time in the Senate will end when my term ends in early January 2019. For the next 14 months, relieved of the strictures of politics, I will be guided only by the dictates of conscience.

It's time we all say: Enough.