In the days following his announcement that he would not be seeking re-election, Sen. Jeff Flake said he's received thousands of reactions in the form of calls and letters from people all across the political spectrum.

"Each letter is distinctive, but all are plaintive, anguished, deeply engaged and urgent," Flake wrote. "They all have in common a feeling of distress that the country has taken a sudden and caustic turn, that we have a president who seems to take pleasure in dividing us."

Flake's words come from an op-ed he penned in the New York Times which was published Monday.

In the piece, Arizona's junior senator called reading the letters one of the "most humbling experiences" of his public life, but not because of the support he received for his speech on the Senate floor back in October.

"I am humbled because until now I didn’t fully grasp the level of anxiety and real pain that exists across the country due to the state of our national leadership," Flake wrote.

Flake said the concerns from those who wrote him stem from the "seeming disregard for the institutions of American democracy."

"The damage to our democracy seems to come daily now," Flake wrote. "And as this behavior continues, it is not just our politics being disfigured, but the American sense of well-being and time-honored notions of the common good."

RELATED: Arizona politicians react to Jeff Flake's announcement to leave Senate

In a rather sharp jab at the current president, Flake acknowledged every president at some point has made poor decisions and has been criticized for taking the country down a "wrong path." But under Trump, he wrote, "we all know that things will not improve."

"When a leader wreaks havoc on our democratic norms, it is not just political Washington that is dragged through the muck," Flake wrote. "When that happens, it is deeply upsetting to people everywhere, almost existentially so, and we all suffer."

Flake ended his op-ed piece by saying the letters reminded him that a democracy needs voices that speak out and to have a vital one, there could be "no bystanders."

"As a conservative, I do not seek conflict with the president of the United States," he wrote. "But the experiences of this year, and particularly of this week, have made me realize that to stand up and speak out is sometimes the most conservative thing a citizen can do."

READ MORE: These reasons may be why Jeff Flake isn't seeking re-election