The day the British government concluded a Withdrawal Agreement with Brussels meant to ensure an orderly, phased exit from the European Union, Boris Johnson strode before the cameras and denounced it as "vassal state stuff."

"For the first time in a thousand years," the future prime minister fulminated in November last year, the U.K. would be forced — for the duration of the proposed transition period, and perhaps for longer — to obey EU laws over which its parliament had had no say. That would be a betrayal of his pledge in the 2016 referendum that Brexit would mean taking back control over the nation’s policy.

Now that Johnson has grabbed the steering wheel from Theresa May and set the country hurtling toward a “do or die” no-deal crashout on October 31, the specter of vassalage once again looms large — not to Brussels but to the United States of Donald Trump.

In his first month in Downing Street, Johnson has spoken to the U.S. president no fewer than 10 times about Brexit and world affairs, according to his office. His foreign secretary and international trade secretary have already been to Washington to plead for an early trade deal. And yet, until this week, he had yet to exchange more than brief courtesy calls with European leaders.

Anyone in any doubt about the U.K.’s new self-inflicted dependence on the U.S. need look no further than the visit earlier this month of National Security Adviser John Bolton, who said the Trump administration would enthusiastically support a no-deal Brexit.

Despite Johnson’s slogans, the U.K. has few foreign policy alternatives to subservience to the United States.

Bolton talked up the chances of an implausibly swift U.S.-U.K. trade deal, which he has no power to deliver and which Democrats in Congress are already vowing to thwart. Crucially, he also spelled out Washington’s first foreign policy demands.

Trump expects the U.K. to renege on the 2015 Iran nuclear deal, which London and its EU partners helped negotiate along with Russia, China and the previous U.S. administration, and align with the U.S. policy of “maximum pressure” on Tehran, including enforcing unilateral sanctions and joining U.S.-led gunboat patrols in the Persian Gulf sea lanes. He also expects Johnson to follow the U.S. in shutting Chinese telecoms giant Huawei out of public tenders for 5G mobile communications infrastructure, a highly sensitive issue on which May was leaning in the other direction but which she left unfinished before leaving office. The U.K. government has said it is waiting to see the implications of Trump's decision to blacklist Huawei.

Magnanimously, Bolton said the White House is not pressuring Britain and was prepared to give it time to come into line.

Veteran British diplomats, past and present, are in no doubt that Trump’s price for helping the U.K. politically and economically after Brexit will be closer alignment with U.S. policies on a range of issues on which London has been broadly in disagreement with Washington and in lockstep with its EU partners in recent years: the Middle East, arms control, multilateralism, climate change and trade.

Facing a potential financial market meltdown, investment strike and currency crisis if it lurches out of the EU without a safety net, Britain will be ill-placed to resist. It may need U.S. help to support the pound or buy U.K. government bonds.

“We are going to find our foreign policy increasingly constrained by economic desperation for free-trade agreements and markets,” a former top U.K. government official said. “Trump is very transactional. There’s no sentimentality. There will be a price and that price will be vassalage.”

Washington may seek British support in its efforts to emasculate the World Trade Organization, the International Criminal Court (a personal Bolton obsession since its inception in 1998) and the Paris climate accords. What if the Trump administration asks London to join it in blocking the European candidate to head the International Monetary Fund?

Indispensable ally?

Despite Johnson’s slogans about an independent Global Britain pursuing ambitious deals with the world’s rising economies, the U.K. has few foreign policy alternatives to subservience to the United States.

Privileged economic ties with China — the goal of ex-premier David Cameron and his chancellor of the exchequer, George Osborne — would fall foul of Trump’s trade war, and it’s hard to imagine London cozying up to Beijing while the communist state is threatening pro-democracy protesters in Hong Kong, a former British colony. Besides, the U.K. is of less interest to China if its financial center is no longer a guaranteed gateway into the EU.

Brexit Britain may end up being a less useful vassal than Washington anticipates except, perhaps, in assisting with Trump's strategy of weakening the EU.

The same applies to Japan, which has spelled out its opposition to Brexit in no uncertain terms. Japanese companies, led by automakers Honda and Nissan, are expected to among the first to divest from the U.K. if it is abruptly severed from the EU’s single market.

Ambitions for a new partnership with India may be stymied by New Delhi’s unilateral revocation of the autonomous status of Indian-administered Kashmir, a territory disputed by Pakistan. Tension over Kashmir could explode onto British streets if the conflict escalates.

On top of these political sensitivities for the U.K., which presided over the bloody partition of India in 1947 at the end of the British Raj, the Indian government has made closer trade ties conditional on more visas for Indians to study in Britain at a time when London is clamping down on immigration.

Neither the Commonwealth — a loose grouping of mostly former British colonies — nor the so-called CANZUK alliance with Australia, New Zealand and Canada, which used to be known as the “white Commonwealth,” offer a serious substitute for the EU’s global clout.

Subordination to the U.S. would not be entirely new for post-Brexit Britain. The default setting of British foreign policy since World War II has been to hug America tight, particularly since the humiliation of being forced by U.S. pressure to withdraw from the Suez Canal in 1956 after a joint invasion with France and Israel against Egypt’s nationalization of the waterway.

The British establishment likes to think it has a “special relationship” with Washington, even if in practice this is only true in the realms of intelligence and cybersecurity. Former Prime Minister Harold Macmillan depicted Britain as playing the civilizing role of Athens to America’s brash imperial Rome. It has long been a tenet of British policy that the U.K. should be at America’s side from Day One when it goes to war — both to secure influence and to position itself as the “indispensable ally.”

That position has been under a cloud since the public backlash against Tony Blair’s participation in the U.S.-led invasion of Iraq in 2003. After parliament rejected British involvement in proposed U.S.-led air strikes on Syria in 2013, the U.S. has increasingly looked to France rather than Britain as its go-to partner in the fight against jihadists in the Middle East and North Africa.

A diminished ally due to lost influence in Europe, Britain’s real defense spending is also likely to decline. A devalued pound will buy less dollar-denominated equipment, and Johnson will face competing demands to fund promises to hospitals, farmers, rail infrastructure and Brexit-hit businesses with less revenue.

The gung-ho instinct to play Robin to America’s Batman will clash with a “little Englander” isolationist streak among many Brexiteers. So Brexit Britain may end up being a less useful vassal than Washington anticipates — except, perhaps, in assisting with Trump's strategy of weakening the EU.

Paul Taylor, contributing editor at POLITICO, writes the Europe At Large column.