Sen. John McCain (R-Ariz.) appears with Mitt Romney, the Republican presidential nominee, in January 2012. (Melina Mara/THE WASHINGTON POST)

In more ways than one, followers of traditional Republican orthodoxy are facing an emotional inflection point this week.

Sen. John McCain (R-Ariz.), at home battling an aggressive form of brain cancer, will not attend this weekend’s Munich Security Conference, an annual gathering of foreign policy leaders from NATO nations that has become a central clearinghouse for global security matters and a celebration of Western values and democratic institutions.

McCain, an avatar of all of the above, has been a regular attendee for decades. Last year, less than a month after President Trump took office, he stole the show with a speech that denounced the new president’s refusal to condemn Russian President Vladi­mir Putin.

“Our fellow citizens seem to be flirting with authoritarianism and romanticizing it as our moral equivalent,” McCain said there last February.

But with McCain’s retreat comes another man’s reemergence: Mitt Romney, his onetime political rival for the 2008 GOP presidential nomination. Romney had been scheduled to launch his campaign for senator from Utah on Thursday, but he delayed the announcement Wednesday evening “out of respect for the victims and their families” of the South Florida high school targeted by a gunman.

It’s not clear how Romney, a heavy favorite to win, would approach his role as a senator, particularly in the era of Trump. His aides say that on the campaign trail he will avoid the role of chief foil to the president.

But at times, Romney has sounded like just that — and a defender of Western values, and a deep antagonist of Putin, and a free-market globalist.

Romney took to Twitter, for instance, to lash out at Trump last month after The Washington Post reported that the president, in a meeting with senators, said that he did not want more immigrants from “shithole” countries such as Haiti or in Africa.

“The poverty of an aspiring immigrant’s nation of origin is as irrelevant as their race,” Romney tweeted. “The sentiment attributed to POTUS is inconsistent [with] America’s history and antithetical to American values.”

Friends of both men say Romney’s willingness to jump back into the political arena provides them with another high-profile antagonist to Trump’s America-first worldview.

Is Romney’s timing important? “Yeah, it is,” Sen. Jeff Flake (R-Ariz.) said.

Plenty of other Republicans on Capitol Hill maintain those traditional Republican values of global dominance and free trade, but most of their voices have been quieted in the era of Trump.

“He’ll have a big impact. He comes with immediate gravitas, credibility and stature, and it will be a whole new power structure I think in the Senate, as people gravitate to him,” Flake said of Romney.

The anti-Trump Republicans need all the help they can get. McCain returned to Arizona before Christmas and has not appeared in the Senate since. Flake is retiring at the end of this year. Sen. Bob Corker (R-Tenn.), after a public dispute with Trump over his behavior related to race riots in Charlottesville, announced that he too would retire.

Now Corker is reconsidering whether to run for reelection, but he would probably do so only if Trump supports his bid — a move that might make criticism of the president more difficult.

In the House, most Republicans have embraced much of Trump’s agenda and have worked to protect him from an investigation into Russian efforts to tip the 2016 campaign in his favor. Speaker Paul D. Ryan (R-Wis.), who initially refused to endorse Trump in 2016, sided against the FBI and Justice Department in favor of Republicans on the intelligence committee in releasing a memo that attempted to undermine portions of the Trump investigation.

A decade ago, in February 2008, Romney withdrew from the Republican presidential primary after losing a bitter and sometimes personal campaign to McCain. But four years later they put that behind them and, early in the 2012 primary, McCain threw his support to Romney.

Both Republicans would go on to lose to Barack Obama in their respective general-election contests, but they have both retained some level of prominence as elder statesmen in their party, particularly on foreign-policy matters.

Senators in both parties say that in world travels, gravitas matters. World leaders take McCain far more seriously than any other senator traveling abroad.

“When John McCain speaks, the world listens,” Sen. Lindsey O. Graham (R-S.C.), McCain’s longtime travel partner, said Wednesday. “He’s got respect from all over the world in terms of foreign policy.”

Graham will be part of the bipartisan delegation in Germany this weekend, as will Sen. Sheldon Whitehouse (D-R.I.), who said he will not recognize the event without McCain.

“I think he founded it,” Whitehouse joked. “He was present at the creation.”

Actually, the security conference was founded in 1963, when McCain was still a young naval aviator. But he has been such a regular that, after his planned address Friday, McCain was slated to receive a special honor Saturday, presented by former vice president Joe Biden.

Whitehouse said that European leaders do not understand Trump or his motivations, which is why they look to McCain’s leadership to reassure them. Whitehouse has his differences with McCain on national security, but he said it’s critical for foreign leaders to hear that some Republicans still believe in U.S. global leadership.

“It’s very important, I mean, particularly when you’re dealing with countries like the ones that we’ll be visiting, that live in the shadow of Russia’s malign influence,” he said.

In his presidential campaign, Trump enjoyed attacking both the 2008 and 2012 presidential nominees.

A few weeks into his bid, Trump said McCain was “not a hero” for enduring 5 1/2  years of imprisonment in Vietnam because he was a bad pilot who got shot down. Later, he called Romney a “stone-cold loser.”

Now, with McCain’s career in its twilight, Romney has a chance to take that mantle as a high-profile defender of conservative GOP ideology and America’s place in the world.

Back in October, after McCain delivered an excoriation of Trump in Philadelphia, Romney lavished praise on the speech.

McCain is, Romney tweeted, a “hero, champion of character and last night, Lincolnesque.”

Last February, McCain did not hide his contempt for Trump’s stance on Russia. “I refuse to accept that our values are morally equivalent to those of our adversaries,” he said in Germany. “I am a proud, unapologetic believer in the West, and I believe we must always, always stand up for it — for if we do not, who will?”

When McCain leaves the stage, the answer to that question may be Mitt Romney.

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