Stephen Miller used to schedule meetings with me in the White House Situation Room. The space is typically used for classified discussion of the highest national significance, but what was odd was that we weren’t discussing anything classified. Stephen just liked a room where he was sure no one could hear his scheming.

That memory came back to me this week, when Miller walked into the West Wing as Donald Trump’s new chief of staff, a promotion handed out days after the Republican defeat in the midterms. Americans will spend the next two years finding out what that means for them. I’d gently suggest that Britain and Europe pay close attention, because I spent almost two and a half years in rooms with this man, and the thing he resents most in the world is the idea that the United States owes anything to anybody, allies most of all.

People who’ve worked with Miller will tell you he’s a caricature of himself, and they’re right. He’s famously paranoid, which is how we ended up in those secure rooms. He’s loyal to Trump in a way that borders on the religious. And he’s ideological to the bone, a true believer in a world where “globalist” is an intentional slur and every treaty, alliance and trade deal is a scam run on the American people.

The caricature was easy to laugh at when he was a thirty-something speechwriter with a shoved-in-lockers axe to grind. Now he runs the building and, I suspect, relishes that he can wield power over his detractors. You know the type.

The messages from former colleagues came flooding in after Miller’s appointment. “I think very few people understand how extreme he is,” one of them wrote. This person had been an attendee at Miller’s wedding and had not spoken out against him, but feared what he’d do now, empowered by Trump.

For allies, that assessment is especially relevant. In my private sessions with Miller when I helped lead the Department of Homeland Security, he mocked our closest partners, berated them and schemed against them – regularly demanding that DHS find pressure points to coerce friendly governments into accepting the administration’s policy positions or complying with Trump’s demands. He was hostile to the core, and we feared his slash-and-burn attitude could result in serious national security setbacks, including with countries on whom we depend to counter-balance our adversaries. Thankfully, there was always someone to check Stephen, whether it was the Secretary of State or the Vice President.

Some have called him an “isolationist”, but that’s the wrong word to describe Stephen. An isolationist wants America out of the world’s entanglements and is content to leave the furniture where it stands. In my experience, Miller wants the furniture broken. What does that mean? Well, anyone who is a keen booster of international institutions — like Nato, the United Nations, the Western trade architecture, legacy intelligence-sharing relationships, or even just the bipartisan tradition of calling London or Berlin before doing something drastic — should be concerned. Miller is averse to much of it and has an almost messianic view of upending the Western world.

He’s also a relentless micromanager, meaning he’s not inclined to let Trump’s more outlandish demands die inside the bureaucracy. One of my colleagues had this experience during the first term, as the White House was trying to get the Education Department to do something obviously repulsive: kick undocumented children out of public schools. When the education secretary, Betsy DeVos, told the White House it would be illegal, Miller rang her up personally while she was travelling in the Netherlands and told her to find a way to do it anyway. 

“Are you afraid of getting sued, Betsy?” he reportedly taunted.

The plan, as her chief of staff later described it to me, was to ignore the law, get sued and litigate it up to the Supreme Court. That’s the Miller method in a sentence. I can vouch for this.

Toward the end of my time in the first Trump administration, Stephen invited me into his second-floor office in the West Wing and showed me a locked drawer in the desk. He said that inside he’d placed draft executive orders for a second term that would test the limits of presidential power. The plan, as he described it, was to issue the orders, weather the incoming lawsuits and take them up to the Supreme Court just to see how far the judicial branch would let Trump go. He grinned as he dubbed the scheme “a shock-and-awe blitz”.

Whether that locked drawer actually contained anything no longer matters – because there’s nothing standing between the man who drafts extreme, fantasy orders and the man who can sign them.

So here’s what I’d expect on foreign policy with Miller running the West Wing, and these are just my educated guesses: a settlement in Ukraine on terms Moscow can live with, imposed rather than negotiated; a sharper pullback from Nato than anything we’ve seen so far, possibly to the point of withdrawal; allies micromanaged by a man who regards consultation as weakness; and a White House where every agency answers directly to him. Senate-confirmed secretaries will be powerless. There will just be Stephen.

Yet I also believe this appointment will fail spectacularly for Donald Trump, because I’ve seen how Miller’s projects tend to end. He drives everything to the extreme and keeps driving until something stops him — and something usually does. Whether it was Trump’s “Muslim Ban” or the foreseeable catastrophe of family separation at the southern border, Stephen’s projects often didn’t survive first contact with reality. Once they were met with public fury and the reality of the rule of law, they were dialled back or halted.

But overseas, there’s no court of appeals. The only thing standing between Stephen Miller and the Western alliance is the Western alliance itself.

I rarely saw Miller back down because someone persuaded him with facts. He only did it when the consequences were unbearable. So my advice to America’s friends is to make it unbearable early, loudly and together. Otherwise you’ll learn what I learned in those windowless rooms — Stephen Miller is not an isolationist, he’s an arsonist.