A Republican knowledgeable about North Korea policy notes that Tillerson “made North Korea a big priority with other countries. He brought it up in almost every meeting.” And in early August, after Pyongyang tested an intercontinental ballistic missile, the Trump administration convinced China and the rest of the UN Security Council to pass its harshest sanctions ever against Kim’s regime.

But on August 11, just a few days after the sanctions were passed, Tillerson noted that, “We have other means of communication open to” North Korea “to certainly hear from them if they have a desire to want to talk.” 11 days after that, Tillerson observed that since North Korea had not launched any missiles since the UN imposed sanctions, “perhaps we are seeing our pathway to some time in the near future having some dialogue.”

A week later, however, North Korea tested a mid-range missile over Japan. For Trump, that did it. Engagement was over. “The U.S. has been talking to North Korea, and paying them extortion money, for 25 years,” he tweeted the next day, “Talking is not the answer!” In August, Trump also began talking in increasingly graphic terms about the “fire and fury” America could unleash on North Korea in the event of war.

For his part, though, Tillerson kept emphasizing negotiations. On a trip to China in late September, he told reporters that, “We are probing, so stay tuned. We ask, ‘Would you like to talk?’ We have lines of communications to Pyongyang.” A New York Times story written from Tillerson’s trip, and sourced to officials “inside and outside government” suggested that during such negotiations, “the promise of scaling” back U.S. and South Korean military exercises “could be dangled” to convince Pyongyang to freeze its nuclear and missile tests. Yet again, Trump slapped Tillerson down. The morning after the Times story, the president tweeted that, “I told Rex Tillerson, our wonderful Secretary of State, that he is wasting his time trying to negotiate with Little Rocket Man...”

It is Trump’s comments torpedoing talks with the North that appear to have alarmed Corker the most. In the Times interview, he said Trump’s “tweets, especially as it relates to foreign policy issues, I know have been very damaging to us” and have “hurt us as it relates to negotiations that were underway.” He specifically rejected the notion that Trump and Tillerson were engaged in “some good cop, bad cop act” in which Trump’s bellicosity strengthened his secretary of state’s bargaining power. And he warned of miscommunication, saying that Trump doesn’t understand the way “the messages that he sends out” are “being received in other languages around the world.”

In this regard, Corker’s fears resemble those of American reporters who have recently been to North Korea. “To go between Washington and Pyongyang at this nuclear moment is to be struck, most of all, by how little the two understand each other,” wrote Evan Osnos last month in The New Yorker. More recently, The New York Times’s Nicholas Kristof declared that, “I’ve been covering North Korea on and off since the 1980s, and this five-day trip has left me more alarmed than ever about the risks of a catastrophic confrontation.” He urged “talks without conditions, if only talks about talks” to prevent a “crisis that escalates.”