It doesn’t matter all that much that Bob Corker and Donald Trump are insulting each other via Twitter. Sooner or later, Trump insults almost everyone. What matters is that Corker, the Chairman of the Senate Foreign Relations Committee and a confidant of the secretary of state, is warning publicly that “we could be heading towards World War III,” presumably with North Korea. The crucial question is why.

It’s possible that in his New York Times interview, Corker got carried away. As former Bush administration National Security Adviser Stephen Hadley told me, “Forces have not been mobilized. The military is still saying diplomacy comes first.”

But it’s also possible Corker genuinely fears that Trump and Kim Jong Un’s blood-curdling rhetoric, combined with ongoing North Korean missile and nuclear tests and American displays of military force, pose a risk of catastrophic miscalculation—war by accident. Reducing that risk requires meaningful communication between Washington and Pyongyang. And Corker—who told the Times that “in several instances” Trump has “hurt us as it relates to negotiations that were underway by tweeting things out”—seems worried that Trump is rendering such communication almost impossible, thus leaving both the U.S. and North Korea flying blind.

Until recently, the Trump administration’s North Korea policy had two faces. They were reflected in the name of the strategy the administration unveiled in April, after two months of interagency review: “Maximum pressure and engagement.” In the name of maximum pressure, Trump urged China to cease propping up North Korea’s economy. He also sent (or claimed to send) an aircraft carrier to the region to scare Kim, and warned of a “major, major conflict.”

But Trump also made it clear he was open to “engagement”—in some ways, more open than his predecessor. In early May, he said that under the right circumstances, he’d be “honored” to meet Kim. (Imagine if President Obama had said that.) Less publicly, the Trump administration reopened something called “the New York channel.” Since it has no embassy in Washington, North Korea’s mission to the United Nations constitutes its only diplomatic presence in the United States. Pyongyang’s men in New York (and only New York; they’re prohibited from traveling more than 25 miles beyond Columbus Circle) aren’t empowered to negotiate with the U.S. But they can relay messages, and had since the 1990s. That changed last July when the Obama administration imposed sanctions that personally targeted Kim and his top associates, and Kim retaliated by closing the New York channel down.

Soon after taking office, the Trump administration reopened it. Joseph Yun, the State Department’s special representative for North Korea policy, began meeting with Pyongyang’s men in Turtle Bay. And he went further. In May, Suzanne DiMaggio, a senior fellow at the think tank New America, organized a dialogue with North Korean officials in Oslo. Yun showed up and talked to the North Koreans himself. As a result of those talks, Pyongyang allowed officials from Sweden (which represents the U.S. in North Korea) to visit Americans detained in the North’s jails. And in mid-June, Yun himself traveled to North Korea to secure the release of the detained American Otto Warmbier, who later died from injuries he sustained in captivity.

Since the Trump administration lacks a permanent assistant secretary of state for East Asian and Pacific Affairs, Yun reports directly to Secretary of State Rex Tillerson. And DiMaggio believes that Yun’s discussions with North Korean officials in Oslo could have turned into “talks about talks,” the kind of quiet, preliminary discussions that laid the foundation for formal, multinational negotiations between the United States and Iran.

Like the Obama administration, which increased economic pressure on Tehran even as it moved towards negotiations, Tillerson throughout the summer worked to put “maximum pressure” on North Korea while simultaneously signaling that such pressure was aimed at improving America’s leverage in its forthcoming “engagement” with Pyongyang.

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.”

What Corker, Tillerson, Osnos, and Kristof understand is that while a diplomatic deal with North Korea may be impossible, improving communication with North Korea is essential to reducing the possibility of accidental war. Kim is likely to test additional missiles. Last week, two Russian parliamentarians who came back from North Korea suggested that Pyongyang would soon test a missile capable of reaching California. Last month, North Korea’s foreign minister suggested his government might test a nuclear weapon over the Pacific, which would constitute the first atmospheric nuclear test in decades. Given its uncertainty about where such a nuclear test would land, the Trump administration might respond by trying to destroy a nuclear-tipped missile on the launchpad.

Kristof has also warned that “a dogfight between a North Korean and an American plane could cause a crisis that escalates.” In late September, the United States sent B1 bombers and F-15C Eagle fighter planes further north along the coast of North Korea than ever before. DiMaggio, who has been talking to officials from Pyongyang for the past two years, warns that, “This combination of heightened military maneuvers plus escalatory rhetoric could signal to the North Koreans that something is imminent and lead to a miscalculation.” In such an atmosphere, she argues, “having a direct channel that can put Trump’s tweets in context,” is crucial. Without one, “North Korea might read them as signaling a preference for war, and respond accordingly.”

Despite Trump’s efforts, DiMaggio does not believe communication channels between the U.S. and North Korea have entirely closed. But she fears his “rhetoric has undercut some of the quiet diplomacy that has taken place.”

That, I suspect, is what Corker fears too. North Korea has nuclear weapons. Soon, it will likely gain the capacity to hit the United States with them. That means the United States, whether it admits it or not, will rely on deterrence to prevent war. Since deterrence involves sending signals to one’s adversaries, it requires communication to work most effectively. That’s why the United States and Soviet Union installed a “hotline” between each country’s leaders after the Cuban Missile Crisis.

Nothing like that exists between the U.S. and North Korea today, but Rex Tillerson is trying to improvise some sort of substitute. Donald Trump, who keeps threatening war and authorizing provocative military maneuvers, is doing his best to make sure that Tillerson fails. That terrifies Bob Corker. It should terrify the rest of us, too.