Kudos to President Trump for meeting with North Korea’s Kim Jong-un in Singapore, and for negotiating what could be the most important arms-control agreement of our time. And kudos to the president for sending Secretary of State Mike Pompeo back to Pyongyang last week to present Kim with an actual plan and timetable for getting rid of that country’s nukes. That’s more than any of Trump’s predecessors had the sense to do.

It’s no surprise that Pompeo’s visit left the North Koreans squawking and the White House scrambling. These sorts of negotiations never go smoothly. But here are the two questions on which the outcome of this agreement — and the safety of our country — will now depend:

Which U.S. government officials will oversee the collection of intelligence about North Korea’s proposed denuclearization program, and then judge whether or not this intelligence confirms that North Korea is in compliance with the Singapore accord?

If the intelligence reveals that North Korea is cheating, how will they tell Trump that Kim’s just played him for a fool?

Monitoring North Korea’s promise to denuclearize will be the job of our country’s intelligence community. This is an alphabet soup of more than a dozen agencies — CIA, NSA, and others most Americans have never heard of. If North Korea really does denuclearize, these agencies will need to confirm the physical demolition of however many nuclear bombs they’ve already got, the permanent shutdown of the facilities that built these bombs and presumably could replace them, and the destruction of North Korean missiles capable of delivering nuclear weapons to overseas targets. Each of our intelligence agencies will have something to contribute to this monitoring effort: the CIA has spies, for instance, while NSA has satellites and other covert listening devices. While the heads of these agencies will play important roles, the job of overseeing what may be the most complex intelligence project in American history will fall to the Director of National Intelligence, former U.S. senator Dan Coats.

How Will Coats Find Out?

Coats’ biggest problem will be making sure that crucial intelligence actually reaches him. It’s nice to believe that all intelligence officials are professionals with absolutely no political biases; who won’t allow their personal views to influence their work. Many are like this, and we’re lucky to have them. But as we’ve just learned from the Inspector General’s report on the FBI’s activities regarding Hillary Clinton’s email, in the real world some government professionals — usually at the upper echelons of power — do allow their political biases to influence how they interpret what they see.

So while many of our career intelligence operatives will indeed be professional and impartial — just like so many of their honorable counterparts at the FBI, who are appalled by the scandal there — some of our top-level spooks and analysts could be so anti-Trump they’ll interpret whatever intelligence they collect in a way that discredits the president’s policy. And those of our spooks and analysts who support the president could be tempted to turn a blind eye to evidence of North Korean cheating. Moreover, in an intelligence community as large and dispersed as ours, much of this in-fighting will take place down in the bureaucracy, invisible to Coats.

This isn’t a new problem for our intelligence community. It was there when Ronald Reagan was president, and here’s one example of what it looked like from the inside: Terrorism was just then emerging as a global issue. The question arose about state-sponsored terrorism; whether some governments were covertly helping terrorists. The president and Secretary of State Alexander Haig publicly accused the Soviet Union of doing precisely this. It became a huge Washington blowup, with the president’s political enemies blasting him and Haig for letting their anti-Soviet views run amok.

Out at Langley, it was business as usual for our spies and analysts. But to William Casey, whom Reagan had appointed as Director of Central Intelligence, and to the aide Casey had brought in to help oversee analysis and manage production of the U.S. National Intelligence Estimates — me — one thing was clear. Some of the CIA’s senior analysts hated Reagan. They thought he was a right-wing nut whose bellicose attitude toward the Kremlin was dangerous. So they didn’t want to give the president any intelligence that would support his positions. A key part of my job was to extract this intelligence from them, then get it to Casey so he could pass it up to the President. Indeed, this is precisely why he’d brought me with him to Langley.

The Photo Was the Proof

The CIA’s position was that there was no evidence to support the allegation of Soviet involvement in state-sponsored terrorism. Then one day a satellite photo landed on my desk of what the photo-interpreters said were two terrorist training camps, one in East Germany and one in another East European Soviet satellite. I called a meeting of our senior Soviet analysts and asked, “Doesn’t this prove, or at least indicate, that the Russians are sponsoring terrorism?”

Their unanimous reply was “We have no evidence of this.”

“Hang on a second,” I said. “These training camps aren’t in some remote frozen region of Siberia. They’re in the middle of Europe. Look at the photo. That’s a shopping center next to the camp, there’s a bus stop, there’s a church where Bach probably played the organ. It isn’t possible that the East German secret police don’t know about this camp. And if they know about it, so does the Kremlin because the KBG knows how often the East Germans change their underwear.”

Dead silence, and the analysts filed out of my office confident that, once again, they had denied the president proof of what he was saying. What happened next was something I don’t think to this day those analysts have realized: I took the photo to Casey and explained to him what it was, and why I thought that at the very least, it lent credence to claims that the Soviet Union was involved in state-sponsored terrorism. Casey nodded, took the photo from me — grabbed it out of my hands would be more accurate — and stored it in what was then the most secret, impenetrable hiding place in the history of American intelligence: the inside left pocket of his suit jacket. He would see that the photo reached Haig and the President.

I got myself another copy of that photo, then took it around to my lower-level counterparts at the State Department, the Pentagon, and the White House. You’ll have to take my word for this, but when you hand over to officials a piece of intelligence that supports their policy, you’re a hero. They thank you, they say nice things about your career prospects, sometimes they even treat you to lunch in the White House mess. But if you give them a piece of intelligence which indicates their policy is about to blow up in their faces because it’s, um, disconnected from reality — things get chilly very fast. You’re no longer a member of the team. The next morning there’s a story in the Washington Post that makes you look like an idiot. You don’t get invited to this year’s Labor Day picnic — you know, the one we all look forward to because everyone who counts is there, including some Washington power-brokers who just might be able to offer you a really terrific job when you leave the administration, for example at a think tank or on a board of directors.

If every piece of intelligence we collect about North Korea points in the same direction — that Kim really is denuclearizing his country — the next few months will be pleasant for Coats and other key intelligence officials, such as the CIA’s newly-appointed director, Gina Haspel. But if intelligence comes in suggesting that Kim is cheating, things will get unpleasant, very fast. Coats, like Casey when he ran intelligence for President Reagan, is at the end of his distinguished and varied career. He probably won’t lose sleep over telling Trump that Kim’s just screwed him. It won’t be so easy for Haspel, who’s spent her entire career at the CIA, to tell Trump or Pompeo they’ve been had; Pompeo had been her boss at the CIA before he was named Secretary of State, and it was on his recommendation that Trump gave Haspel the top slot.

Pieces of Intel Aren’t Enough

Whatever the intelligence we collect about North Korea suggests — and it’s implausible that every single piece of intel will point in the same direction — there’s more to doing intelligence than just dropping selected bits and pieces on policymakers’ desks. (Or leaking pieces of intelligence to selected reporters, which is already happening.) It’s too easy for policymakers to take what they like and ignore what they don’t like. The ultimate responsibility of our intelligence community — and its most valuable contribution to our security — is to reach and then convey to key policymakers a comprehensive judgment of what all the bits and pieces mean:

Is North Korea really giving up its nukes and the ability to replace them. Is Kim trying to make this happen as he promised Trump, but running into opposition from his military leaders. Are the North Koreans taking some cosmetic steps to trick us into believing they’re doing what they’ve promised, but working covertly to preserve their nuclear bombs. What are the Chinese and the Russians doing either to help Kim, or hinder him, or to find some way of using all this to weaken the U.S.

The best way for our intelligence community to paint a clear, comprehensive picture of what Kim is doing and of what’s actually going on in Pyongyang — and in Beijing and Moscow — is through a National Intelligence Estimate. An NIE is the most authoritative document produced by our intelligence community. Within the national security establishment, an NIE can have the impact of a decision by the U.S. Supreme Court. That’s because an NIE includes not only the key pieces of intelligence that have been collected about a foreign policy issue but, far more importantly, the judgment of the DNI and the heads of every other intelligence agency of what this intelligence means. In this sense, an NIE is the final word.

Just like a Supreme Court decision, an NIE is especially powerful when its judgment is unanimous; when the heads of all our intelligence agencies agree on the meaning of what’s been collected. Of course, it’s easy to produce an NIE which shows unanimous agreement. You just write a judgment that’s so obvious no one can take issue with it: We believe the coming months will be turbulent in the Mideast. The issue of immigration will continue to dominate politics in Europe. The newly reelected president of Turkey will now attempt to consolidate his power. The advantage to judgments like these is that when you resign and publish your memoirs, you can claim — accurately — that you were never wrong. The problem, of course, is that obvious judgments are useless to policymakers.

When an NIE provides a judgment that’s specific, unanimity is just as rare as in a Supreme Court decision. And that’s good because it’s the dissents that provide an understanding of what an intelligence disagreement is about. When the head of one intelligence agency takes one meaning from all the intelligence that’s been collected, while the head of another agency sees the same facts differently — well, that gives policymakers something to think about and discuss as they assess whether to continue their policy because it’s working, or whether to modify or even abandon their policy because it may be about to collapse.

How Casey Did It

Just as the Chief Justice presides over the Supreme Court justices as they debate among themselves over the constitutionality of some law, the DNI presides over the intelligence agency chiefs as they debate and argue among themselves over the meaning of the intelligence that’s been collected. But unlike Supreme Court justices, who are appointed for life and can safely ignore the Chief Justice’s opinions, the heads of our intelligence agencies are unlikely to keep their jobs if the DNI wants them removed.

It takes a strong, confident, intellectually honest DNI to assure that intelligence officials who disagree with him aren’t stifled or shoved aside. This is a good description of Bill Casey, and here’s one more example of how he worked:

We were completing the final draft of an NIE about Soviet nuclear activities, and — for once — we seemed to be cruising toward a unanimous judgment that Casey himself had engineered. At just about the last minute, the director of the Defense Intelligence Agency sent over a dissent which, obviously, reflected the views of our top military officials. They were raising an important point. But the dissent itself was poorly written — long, rambling, so technical it was unlikely the President or any of his national security team would be able to grasp what the Pentagon officials were trying to say. If we just put their dissent into the NIE, it wouldn’t have had much of an impact on the judgment that Casey favored.

It was tempting to do that, but that isn’t how Casey worked. He handed the DIA dissent to me and said, “Get over to the Pentagon and meet with these guys. They’re warriors, not wordsmiths. You sit down with them, figure out what they’re trying to say, then re-write the dissent so that it’ll be clear.” And that’s what we did.

There’s one crucial difference between a Supreme Court decision and an NIE. A Supreme Court decision is the law of the land, and not even a president can ignore it. An NIE is merely the best judgment of our intelligence community. You cannot make a president obey an NIE. You cannot even make him read it. And there’s a huge difference between being briefed about an NIE by some aide — who may put his own spin into the briefing — and sitting quietly, alone, and reading the entire document to truly understand it.

A lot of words have been used to describe Donald Trump since the day he rode down that escalator in Manhattan and stepped into political history, but “modest” and “humble” aren’t among them. No one will be surprised to learn one day that his third-grade teacher wrote a note on his report card that “Donald doesn’t respond well to criticism.” This president isn’t going to be happy with an NIE that says anything other than that Kim is doing precisely what he promised he’d do when he and Trump met in Singapore

It’s possible that Kim is a man of his word; that he really wants to denuclearize his country and has the political clout in Pyongyang to make it happen. Stranger things have happened in politics. But there will be lots of bumps and glitches along the way; there always are. This means our intelligence community is heading into one of the most complex intelligence collection projects — and one of the nastiest fights with policymakers — in American history. Let’s hope that Coats and his colleagues have the smarts to grasp the meaning of whatever they collect about Kim’s denuclearization activities. And if he’s cheating, let’s hope they have the guts to tell the President what they’ve found no matter how badly he may take it.

Herbert E. Meyer served during the Reagan administration as Special Assistant to the Director of Central Intelligence and Vice Chairman of the National Intelligence Council. He is author of the booklet Why is the World So Dangerous.