On Sunday, June 3rd, Senator Jeff Merkley, an Oregon Democrat not previously recognized for his social-media savvy or immigration advocacy, rang the front doorbell at a former Walmart in Brownsville, Texas, whose parking lot was plastered with “Keep Out” signs. Merkley had already seen dozens of young kids held in dog-kennel-like cages at a processing center an hour away, in McAllen, and now was there in Brownsville on a hunch, having been told that hundreds of other young children, who had been separated from their parents, were being held in the former Walmart. Merkley’s staff streamed his encounter with grim-faced employees and local police on Facebook Live. In a twenty-five-minute exchange that became a viral sensation, the employees and officers refused to let the rumpled Oregon lawmaker in as he patiently lectured them on American’s history of welcoming immigrants.

By the time Merkley flew back to Washington, the following day, the video had been viewed more than a million times and the White House had gone into full attack mode against the two-term senator, blasting him in a statement for “irresponsibly spreading blatant lies about routine immigration enforcement.” But as the facts spilled out in the ensuing days, it quickly became clear that an anything-but-routine new Trump Administration policy had led to thousands of migrant children being separated from their families. Merkley triggered a national political uproar with his senatorial fact-finding trip gone viral.

On Wednesday, I sat down with Merkley in his office on Capitol Hill just a few minutes after President Trump signed an executive order ostensibly rolling back his own Administration’s family-separation policy, the same one Trump’s White House had insisted did not exist. This was the first time in Trump’s Presidency that he had actually been forced to back down from a significant policy by public pressure, as televised images of children in cages and leaked audio of wailing toddlers horrified even staunch immigration opponents in Trump’s own party. Many were calling it the worst blunder of Trump’s Presidency, his Hurricane Katrina—a historic P.R. disaster, a political mistake for the ages.

All of which meant that Merkley was now the Man Who Stared Down Donald Trump, arguably the first Democrat to do so effectively. As we talked, Merkley was clearly still outraged. A biting Trump critic previously best known as the only Democratic senator to back Bernie Sanders over Hillary Clinton in the 2016 Democratic primaries, Merkley called Trump’s policy “child abuse,” and seemed angry, in his very low-key way, about the White House’s “massive smear campaign” against him. Tall, soft-spoken, and clad in a slightly too large gray suit, Merkley had previously clashed with Republicans, in 2017, when he seized the Senate floor for a long, losing, sort-of filibuster against Trump’s Supreme Court nominee, Neil Gorsuch. But Merkley had never before become a target of the White House attack machine. “They were, like, ‘There’s no cages, he’s lying, he’s making this up,’ ” he pointed out in our interview.

Merkley, though, wasn’t taking a victory lap. Trump was unrepentant, and his White House had not clarified what, exactly, was in the executive order. Endless rounds of court fights and congressional negotiations seemed imminent. “I’m not sure what’s in it,” Merkley said, sitting in a leather chair in his office; outside his door, phones were ringing off the hook, with constituents wondering what they could do to stop children from being separated from their parents. Yet Merkley worried that, instead of changing course, Trump would devise another policy that was hardly better for children. “It sounds like the handcuffs-for-all strategy,” he told me. “So now we go from one strategy that hurts children to another strategy that hurts children.”

The politics of it were equally murky. Trump was already busy claiming credit for ending a controversy his own policy had created, and many Democrats were concerned that Trump’s executive order was not so much a reversal as a tactical retreat. In fact, it turned out, this was their fear from the beginning. I asked Merkley what his spotlight-loving Democratic colleagues had thought of his viral moment exposing the Trump Administration. The story had exploded, Merkley recalled, but not everyone was happy about it. Some of the other senators were shocked, telling him, “Oh, my God, I can’t believe that they’re really doing it.” But others, Merkley told me, quickly saw political peril. “There were folks saying, ‘My goodness, shifting the attention from health care to immigration is a huge political mistake.’ ”

Senator Jeff Merkley said he considers Trump a “fear” candidate from a Party that had learned to run what he called the “three-terrors strategy”: pick three issues that scare the American public, and emphasize them at all costs. Photograph by Sergio Flores / Bloomberg / Getty

What if they were right? Other than perhaps Trump’s hard-line immigration adviser, Stephen Miller, few believe that images of distraught children will actually help Trump politically. The policy was clearly vastly unpopular with the American public, with opinion polls suggesting that two-thirds of the country opposed it. It could prove particularly unpopular in some of the swing suburban districts that could determine whether Republicans keep control of the House of Representatives this fall.

There are, nonetheless, some uncomfortable facts that Democrats who see the issue as an unmitigated win need to face. For starters, hours before he pulled the plug on his Administration’s policy, and after weeks of other controversies, Trump hit his highest approval ratings since his Inauguration. According to Gallup, forty-five per cent of Americans approved of the job he was doing, which is still a low figure by historical standards, but is arguably strikingly high for such a divisive figure. The President’s endless bashing of undocumented immigrants and his vow to toughen “Boarder security,” as he spelled it in a recent tweet, is a key reason.

Trump’s ability to gin up fears about illegal immigration, more than perhaps any other issue, won him the White House. Headed into a midterm election that will be won by the political party that can better rally its base, Trump has remained determined to talk about immigration, even when others in his party have resisted. Indeed, Republican leaders on Capitol Hill were furious with Trump as the immigration controversy spiralled out of control this week—a time they had planned to spend celebrating the G.O.P. tax cut, along with the general strength of the economy, which they hope to make the centerpiece of their fall campaign.

On Monday, as the political pressure on Trump was escalating, I met with Kristen Soltis Anderson, a Republican pollster who has advised G.O.P. leaders about this fall’s elections at a couple of recent retreats. Trump, she told me, had a “freakishly stable” approval rating; in such a polarized moment, people know where they stand on the President. She said that, unlike in previous midterm elections in which the incumbent President’s party has done poorly, voter enthusiasm for Trump has remained strong among Republican voters, even as a blue wave of Trump-hating Democrats has been building. “The question is,” Anderson told me, “if the blue wave is coming, have Republicans built a large enough wall to stop it?” New Pew Research Center data this week underscored her point, finding that voters in both parties are more motivated to vote than they were at any time in the previous twenty years. The Democrats’ advantage on enthusiasm, Pew found, is significantly weaker than it was in the previous election cycles when their party scored big.