Arizona Senator Jeff Flake said Tuesday he will not seek reelection, and gave an extraordinary rebuke on the Senate floor to President Donald Trump and the rightward shift of the Republican party.

These forces, Flake told his colleagues, have made his path as a to the Senate nomination increasingly narrow as a conservative standard bearer, and he would rather step aside than remain complicit, both with the evolving viewpoints and the calls for unequivocal support of President Trump.

“I have decided that I will be better able to represent the people of Arizona and to better serve my country and my conscience by freeing myself of the political consideration that consumed far too much bandwidth and would cause me to compromise far too many principals,” he said on the Senate floor, adding that he would conclude his service in the Senate in January of 2019.

Flake is the second Senator to announce his retirement this cycle; Tennessee Senator Bob Corker, with whom Trump has been openly feuding, announced in September he would not seek reelection. Corker, who supported Trump during the 2016 election, said on Tuesday that he would not make that same decision again if given a do-over, that the President was a poor role model for the country’s children and that he has “great difficulty with the truth.”

Flake’s remarks seemed as much a call to action for his colleagues to rebuke the President and his rhetoric as they were an announcement of his future plans. Although he never explicitly mentioned Trump by name, he cited how “personal attacks, the threats against principles, freedoms, and institutions, the flagrant disregard for truth or decency” are emanating from the executive branch of government, and that the chamber has an obligation to speak up because it is threatening democracy.

“If we simply become inured to this condition, thinking that this is just politics as usual, then heaven help us,” he said. “When the next generation asks us, Why didn’t you do something? Why didn’t you speak up? — what are we going to say?—I rise today to say: Enough. We must dedicate ourselves to making sure that the anomalous never becomes normal.”

His past criticism of President Trump, he explained, has stemmed from that obligation.

“I am aware that a segment of my party believes that anything short of complete and unquestioning loyalty to a president who belongs to my party is unacceptable and suspect,” he said. “If I have been critical, it not because I relish criticizing the behavior of the president of the United States. If I have been critical, it is because I believe that it is my obligation to do so, as a matter of duty and conscience.”

Before taking the Senate floor, Flake had conveyed these sentiments in an interview with the Arizona Republic. “There may not be a place for a Republican like me in the current Republican climate or the current Republican Party.” He also told the Republic that the primary voters he would have needed to win over are concerned about candidates’ allegiance with Trump, and he was unwilling to falsely throw unequivocal support behind the President.

The open seat provides another opportunity for the Democrats to regain a majority in the Senate, but could also end up getting filled by a more right-wing and Trump-oriented member of the Republican party. The Senator was facing a primary challenge from Kelli Ward, a former state Senator who had unsuccessfully challenged Senator John McCain in 2016. Ward was recently endorsed by former White House strategist Steve Bannon, who has vowed a self-declared “war” on the Republican establishment.

Shortly after Flake finished his speech, Ward wrote on Twitter that his decision was a win for Arizona’s constituents. “They deserve a strong, conservative in the Senate who supports POTUS & the ‘America First’ agenda. Our campaign proudly offers an optimistic path forward for Arizona & America. #MAGA,” she wrote.

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Write to Alana Abramson at Alana.Abramson@time.com.