Theresa May and Donald Trump Mark Wilson / Getty

Trump's defense secretary warns US could "moderate" its NATO commitment

May had heralded Trump's "100% commitment" to NATO

Downing Street saw commitment as key leverage in Brexit plans

Comments will wreck May's hopes of being a bridge between the EU and US.

LONDON — "Mr President, I think you confirmed that you are 100% behind NATO," Theresa May said to Donald Trump as they began their joint White House press conference last month.

"Today we have reaffirmed our unshakable commitment to this alliance."

Just one month on and Trump's "unshakeable" commitment has been shaken to its core.

In a speech to America's NATO allies in Brussels on Wednesday, Trump's Defense Secretary James Mattis warned that the US may "moderate" its commitment to NATO, unless other members increase their contributions.

"If your nations do not want to see America moderate its commitment to this alliance, each of your capitals needs to show support for our common defense," he said.

The comments throw open the previously inconceivable possibility of America weakening or even withdrawing its long-held commitment to defending its European allies.

It is a shattering blow, not only to those European countries currently looking nervously towards Moscow, but also to the UK government's hopes of forging a new special relationship with the Trump administration.

A bridge to nowhere

At the time Trump's "commitment" to NATO was seen by Downing Street as one of the biggest achievements, not only of May's US trip but of her entire premiership. It was loudly boasted of by May and her ministers both in the House of Commons and around the world. When May travelled to the EU summit in Malta earlier this month she did so with the explicit intention of using this apparent commitment to leverage Britain's position in Brexit negotiations.

Prior to her visit, one Downing Street source told journalists that "the Prime Minister will brief EU leaders on her recent visit to the United States of America – where she secured a guarantee from President Trump that he was 100% supportive of NATO."

"She will say that this guarantee – and the recognition of NATO as the bulwark of our collective defence — underlines the importance of strong cooperation on defence and security. "

For the UK government, Trump's "guarantee" on NATO underlined what they saw as Britain's biggest strength in Brexit negotiations — it's contribution to Europe's collective security and intelligence apparatus.

May hoped she could use this "commitment" to position herself as the transatlantic bridge between Trump and the EU.

But for European leaders who had already publicly identified Trump as one of the great threats facing the EU, there seemed little benefit in having a go-between with Trump. As the Lithuanian President Dalia Grybauskaitė told Sky News: "I think there is no necessity of bridges."

"Today we are communicating with the United States mainly on Twitter."

Diverging interests

With each passing week, the wisdom of May tying herself so closely to the Trump administration looks more and more questionable. Whether it be his policy on NATO, climate change, the Middle East peace process, or the future of the EU itself, Trump's international agenda is in almost all respects in direct opposition to long-standing British foreign policy.

The prime minister's gamble that a sympathetic approach to the new US administration would draw concessions was in some respects understandable. However, it relied on the assumption that Trump is a rational and consistent player on the world stage, whose commitments, which if not permanent, could at least be relied upon to last more than a few weeks.

After Mattis' comments on NATO, that assumption now looks increasingly naive.