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It was the kind of performance that has made Mike Pence’s career.

Speaking with reporters yesterday in Arizona—his voice slow with that wholesome midwestern drawl, his eyebrows lifted more in sorrow than in anger—the vice president came valiantly to the defense of his persecuted boss amid growing controversy over President Donald Trump’s phone call with his Ukrainian counterpart. “One of the main reasons we were elected to Washington, D.C., was to drain the swamp,” Pence explained, sounding perfectly sincere as he recast Trump’s efforts to pressure a foreign government into investigating his political rival as a bold stand against corruption.

Such ostentatious displays of water-carrying are not new for Pence. But this time the stakes were higher. The Washington Post had recently published a story citing anonymous “officials close to Pence” who appeared to be distancing him from Trump’s escalating Ukraine scandal. To many observers in Washington—myself included—the story was evidence that the two men were not entirely on the same page. Pence’s maneuvering yesterday may have temporarily deflated that narrative, but it also illuminated the fraught nature of his relationship with Trump.

In any embattled White House, an ambitious vice president can run the risk of turning radioactive. Every word he utters in public is dissected, every move searched for signs of a coming coup. Pence, of course, has labored strenuously to perform his loyalty to Trump. But with an impeachment battle raging, and a president burrowing deeper each day into paranoid bunker mode, the fragility of their partnership could soon be on full display.

High regard for Pence among congressional lawmakers could be an especially tender pressure point for the president. One senior Republican Senate staffer, who requested anonymity to describe the situation candidly, told me, “If it was just a matter of magically snapping their fingers … pretty much every Republican senator would switch out Pence for Trump. That’s been true since day one.”

This week isn’t the first time we’ve seen signs of a potential rift. Last year, The New York Times reported that Trump was privately asking allies whether they thought Pence was loyal. More recently, rumors have circulated that the president might replace Pence on the 2020 ticket with former United Nations Ambassador Nikki Haley. And in a news conference last week, Trump voluntarily dragged his vice president into the Ukraine mess by suggesting that journalists look into the calls Pence had made to President Volodymyr Zelensky.

But the roots of Trump’s distrust can be traced back to the final weeks of the 2016 election, when the Access Hollywood tape became public. In the uproar that followed, Pence did not jump to his running mate’s defense. Instead, he retreated from the campaign and issued a disapproving statement: “I do not condone his remarks and cannot defend them.” Anonymous quotes began popping up in the press describing Pence as “beside himself” over Trump’s remarks. And as I would later report in a profile of the vice president, Pence made it clear to the Republican National Committee that he was ready to take Trump’s place at the top of the ticket. (A spokesperson for Pence has denied this.) I wrote:

Republican donors and party leaders began buzzing about making Pence the nominee and drafting Condoleezza Rice as his running mate.

Amid the chaos, Trump convened a meeting of his top advisers in his Manhattan penthouse. He went around the room and asked each person for his damage assessment. [Reince] Priebus bluntly told Trump he could either drop out immediately or lose in a historic landslide. According to someone who was present, Priebus added that Pence and Rice were “ready to step in.”

This episode has not been forgotten by certain Trump loyalists, who believe Pence has shown he will prioritize his own political interests over the president’s if necessary. As one former Trump adviser told me in 2017, “I don’t think he goes down with the ship.”

Of course, the ship is still a long way from sinking. Even if the House impeaches Trump, it remains unlikely that the Senate will vote to remove him from office. But many of the traits that make Pence valuable to Trump now could make him a threat if the dynamics change.

On Capitol Hill, where Trump’s fate may be decided, Pence is far more popular than the president. Doug Heye, a Republican strategist who worked for more than a decade in Congress, told me the lawmakers he’s talked to are exhausted by the president’s behavior. “Everywhere they go, there’s a mic in their face and a reporter saying, ‘Defend what Trump just did,’” Heye said. If Pence ascended to the Oval Office, “it would make the lives of every Republican member easier.”

That sentiment was echoed by the conservative talk-radio host Erick Erickson, who tweeted earlier this week that he’s “starting to encounter Republicans who wonder if maybe the President should step aside for Pence. They’re absolutely in the minority on the GOP side, but there does seem to be a fatigue setting in—tired of always fighting and always having to defend.”

Erickson, who speaks regularly with conservative grassroots leaders and elected officials, elaborated on this point in an email to me. “These are activists who like Trump, but they’re just worn out,” he said. “I have talked to a handful of politicians who would never say anything publicly, but they do think 2020 is going to be tough for Trump, and Pence could neutralize some of the antagonism.”

Among Trump’s religious supporters, meanwhile, many still dream of a Pence presidency. Richard Land, the president of the Southern Evangelical Seminary, told me he understands those conservative Christians who are longing to see Pence in the Oval Office. For many reluctant Trump voters on the religious right, after all, Pence was the real draw in 2016. But reaching that outcome through impeachment, he worried, would be “extremely divisive for the body politic.”

Besides, Land, who joined Trump’s evangelical advisory committee during the campaign, said he believes that Pence has been a “positive influence” on the president. “I am told on reliable authority that they meet together frequently, pray together … [Trump] is a different person than he was three years ago. He’s just a more spiritually sensitive person,” Land said. “I attribute that to some degree to Mike Pence.”

Laudatory talk like this from conservative evangelicals has prompted some pundits to suspect that Trump doesn’t need his Bible-toting running mate anymore to maintain his religious base. But when I put that notion to Land, he was adamant that the Trump-Pence ticket needs to remain intact.

“Removing Pence and picking someone else in the second term would send the signal that evangelicals may not have the same place at the table,” he warned. “I think it would be a grave political miscalculation.”

For now, at least, both Trump and Pence seem to need each other for political survival. But theirs has always been a marriage of convenience—and the coming months will test the strength of that union.

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