Condemning the nastiness of Republican politics in the era of President Donald Trump, Sen. Jeff Flake on Tuesday announced he will serve out the remainder of his term but will not seek re-election in 2018.

The bombshell, which Flake, R-Ariz., delivered Tuesday afternoon on the Senate floor, will further roil Republican hopes of keeping the party's 52-seat Senate majority in the midterm elections of Trump's first term, when the president's party historically loses seats in Congress.

It also likely will upend the race for Flake's seat. Flake, who is among the Senate's more prominent critics of Trump, had been struggling in the polls.

He told The Arizona Republic ahead of his announcement that he had become convinced "there may not be a place for a Republican like me in the current Republican climate or the current Republican Party."

MORE: Read the full text of Sen. Flake's speech

'Here's the bottom line ...'

Flake said he has not "soured on the Senate" and loves the institution, but that as a traditional, libertarian-leaning conservative Republican, he is out of step with today's Trump-dominated GOP.

"This spell will pass, but not by next year," Flake said.

Among Republican primary voters, there's overwhelming support for Trump's positions and "behavior," Flake said, and one of their top concerns is whether a candidate is with the president or against him. While he is with Trump on some issues, on other issues he is not, Flake said. And Trump definitely views Flake as a foe, having denounced him publicly and called him "toxic" on Twitter.

"Here's the bottom line: The path that I would have to travel to get the Republican nomination is a path I'm not willing to take, and that I can't in good conscience take," Flake told The Republic in a telephone interview. "It would require me to believe in positions I don't hold on such issues as trade and immigration, and it would require me to condone behavior that I cannot condone."

As of Sept. 30, Flake's campaign had $3.4 million on hand. He has continued to raise money — as recently as Thursday, former Secretary of State Condoleezza Rice headlined a fundraiser for him in Arizona.

Flake said he had ruled out running as an independent rather than a Republican, saying he didn't think that was a viable strategy. He also said he has "no intention" of making a presidential run. Asked during a CNN interview whether he would entertain challenging Trump in 2020, Flake said, "I won't go there. That's a long time away."

Senate race opens up

Kelli Ward, the former state senator from Lake Havasu City who lost her primary challenge last year against Sen. John McCain, has emerged this year as the top GOP alternative to Flake.

But other names have been mentioned as possibilities: Arizona State Treasurer Jeff DeWit, former Arizona Republican Party Chairman Robert Graham and Arizona Board of Regents member Jay Heiler. Lesser-known Republicans Craig Brittain and Nicholas Tutora also have filed paperwork with the Federal Election Commission and are running.

But Flake's exit is sure to entice bigger Arizona Republican names to take a fresh look at the GOP Senate race.

Steve Bannon, Trump's controversial former White House strategist, has embraced Ward as part of his national "open revolt" against Senate Majority Leader Mitch McConnell, R-Ky., and the GOP establishment. But other Republicans have warned that Ward is a weak candidate whose nomination would jeopardize GOP chances of holding Arizona's Senate seat.

"Arizona voters are the big winner in Jeff Flake's decision to not seek re-election," Ward said in a written statement. "They deserve a strong conservative in the U.S. Senate who supports President Trump and the 'America First' agenda. Our campaign proudly offers an optimistic path forward for Arizona and America."

The winner of the Aug. 28 Republican primary could face Rep. Kyrsten Sinema, D-Ariz., considered the Democratic Senate primary front-runner.

"It’s been an honor to know and serve with Jeff," Sinema said in an emailed statement to The Republic. "He is a man of integrity and a statesman who is true to his convictions – an Arizonan through and through. I wish he and (his wife) Cheryl and their family the very best.”

Senate Minority Leader Chuck Schumer, D-N.Y., praised Flake as "one of the finest human beings I've met in politics."

"He is moral, upright, and strong and he will be missed by just about everybody in the Senate," Schumer said in a written statement.

Bannon, who is now executive chairman of Breitbart News, was quoted by the New York Times late last month as saying if Flake "doesn’t get a better poll in the next 30 days, you’re going to see him step down or the establishment is going to make him."

Flake said he felt no pressure from McConnell or establishment Republicans to quit the race and insisted that he's not bothered by the thought that Trump and Bannon will crow victory.

"They can say whatever they want to say," Flake said.

Dramatic Senate speech

Flake publicly announced his intentions in a Senate floor speech that began around noon Arizona time.

In his speech, Flake gave a blistering critique of the "coarseness of our national dialogue" that has defined the Trump era, saying it should never be accepted as "the new normal."

"We must never regard as 'normal' the regular and casual undermining of our democratic norms and ideals," Flake said. "We must never meekly accept the daily sundering of our country — the personal attacks, the threats against principles, freedoms, and institutions, the flagrant disregard for truth or decency, the reckless provocations, most often for the pettiest and most personal reasons, reasons having nothing whatsoever to do with the fortunes of the people that we have all been elected to serve.

"None of these appalling features of our current politics should ever be regarded as normal," he said.

McConnell, the Senate majority leader, praised Flake after his floor speech.

"We regret to hear that our friend from Arizona will conclude his Senate service at the end of his six-year term," McConnell said. "And I'd like to say ... on behalf of myself and I think many of my colleagues, we've just witnessed a speech from a very fine man, a man who clearly brings high principles to the office every day and does what he believes is in the best interest of Arizona and the country."

Flake said he had alerted McCain about his decision before going public. And the senior senator spoke from the Senate floor shortly after Flake concluded his remarks.

McCain called Flake "a man of integrity and honor and decency and commitment to not only Arizona, but the United States of America" and said it has been one of the "great honors" of his life to serve with him.

"I have seen Jeff Flake stand up for what he believes in, knowing full well that there would be a political price to pay," McCain said.

Sen. Bob Corker, R-Tenn., an ally of Flake's who also has been publicly fighting with Trump, announced Sept. 26 that he would not seek a third Senate term.

The White House characterized Flake's speech as petty.

Sarah Huckabee Sanders, the White House press secretary, said that the Flake and Corker retirements are a reflection of Americans’ public support of the president — and not these Republican senators. It shows “the support is more behind the president than it is behind these two individuals," she said.

Sanders said the senators should be “doing their job instead of all this grandstanding.” ... “Their loyalty should be to the American people. ... I hope we’ll see that in their votes.”

Rift formed with some in GOP

Flake, whose poll numbers have been tanking for at least a year, has publicly sparred with Trump since he emerged as a presidential contender in 2015. Flake refused to endorse or vote for Trump and, during the campaign, was a frequent critic of Trump's tone, tenor and key policy proposals, such as a border wall.

THE WALL | NEWSLETTER: Sign up to receive a free weekly email roundup of news about the border, immigration and the proposed border wall

Flake further antagonized Trump and the president's supporters this summer by publishing a book, "Conscience of a Conservative: A Rejection of Destructive Politics and a Return to Principle," that took the Republican Party to task for embracing protectionism, nationalism and other tenets of "Trumpism" at the expense of traditional Goldwater-Reagan GOP values.

Flake, 54, was first elected to the Senate in 2012, winning a hard-fought general election against former Surgeon General Richard Carmona after defeating GOP primary opponent Wil Cardon.

Prior to that, Flake served six terms in the House starting in 2001.

Something of a political maverick, he routinely angered fellow Republicans by highlighting their spending of taxpayer money on parochial priorities.

While in the House, Flake’s office ridiculed questionable pork projects with a series of “Egregious Earmark of the Week” news releases that usually included corny jokes and bad puns. In 2006, Flake was profiled by CBS’ “60 Minutes” in a flattering segment that compared him to the principled Jimmy Stewart character in the classic 1939 movie “Mr. Smith Goes to Washington.”

His reform efforts are credited with helping lead to an earmark moratorium on Capitol Hill. "If I'm remembered as the guy who killed earmarks, that's a great thing," Flake told The Republic in 2012.

Flake took up other fights during his years on Capitol Hill.

Throughout his 17-year political career, Flake has championed comprehensive immigration reform. However, Congress hasn't come to terms on the issue and Flake's bipartisan work on legislation in the House and Senate alienated many grass-roots conservative activists who consider a pathway to citizenship for immigrants without legal status to be "amnesty."

Flake was a free-trader who believed that the economic embargo against Cuba, which dated to President John F. Kennedy’s administration and was part of the U.S. effort to stop dictator Fidel Castro’s brand of communism from spreading to other countries in the region, had long ago outlived its usefulness. Flake worked for years to ease travel restrictions to Cuba, usually siding with Democrats on the issue and, early in the 2000s, drawing the ire of President George W. Bush’s administration and House GOP leaders. He found an ally on the Cuba issue in President Barack Obama.

He also worked with Democrats on legislation aimed at strengthening protections for civil liberties.

In 2006, Flake helped stop powerful Rep. Tom DeLay, R-Texas, who was facing criminal prosecution at the time, from ever returning to his job as House majority leader.

A chilling day for Flake

In June, Flake was practicing with the congressional Republican baseball team on a field in Virginia when a gunman opened fire on the group. Flake was unhurt, but House Majority Whip Steve Scalise, R-La., was seriously injured. The gunman was killed at the scene.

Flake told The Republic at the time that amid the hail of bullets he had been unsure whether a congressional security detail at the ball field had also been killed.

"For a while, our security detail was firing, and I didn't know if it was friendly," he said. "I kept yelling, 'Are you friendly? Are you friendly?' And he yelled back, 'Yes.' And I saw that it was Steve Scalise's detail. He happened to be at the practice, thankfully, or we wouldn't have had a detail. (As a member of House GOP leadership) he's the only one who has one."

For many, the politically motivated shooting underscored the level of anger surrounding politics.

By withdrawing from his re-election race, Flake is breaking from Arizona's tradition of long-serving U.S. senators, including Democrat Carl Hayden and Republicans Barry Goldwater and McCain.

Only one other senator from Arizona served just a single six-year term: Republican Ralph Cameron, who was elected in 1920 and ousted by Hayden in the 1926 election.

TALKING POLITICS: Listen to our Arizona politics podcast, The Gaggle, on Apple Podcasts, SoundCloud, Stitcher or Google Play.

Ronald J. Hansen and Yvonne Wingett Sanchez of The Republic and Eliza Collins, Erin Kelly and Heidi Przybyla of USA TODAY contributed to this story.

Nowicki is The Republic's national political reporter. Follow him on Twitter, @dannowicki.

READ MORE:

Why Sen. Jeff Flake is stalling relief for hurricane-devastated Puerto Rico

Bannon endorses Ward, signaling Trump supporters have settled on her

Flake bill links DACA fix with money for Trump border wall