The spirit of Thatcherism is alive and well in America’s reenergized conservative movement. In Washington last month, former South Carolina Gov. and former U.S. Ambassador to the United Nations Nikki Haley evoked the memory of Britain’s Iron Lady while delivering the Margaret Thatcher Freedom Lecture at The Heritage Foundation in the heart of America’s capital.

In her powerful address, Mrs. Haley spoke of her deep-seated admiration for Britain’s first woman prime minister and the relevance of Margaret Thatcher’s free-market ideals and conservative principles to America today. She also called on the United States to embrace Brexit, advance a U.S.-U.K. free-trade deal and strengthen the Anglo-American Special Relationship, all of which will be music to the ears of British Brexiteers.

In contrast to President Biden, Mrs. Haley believes America must strengthen its alliances and partnerships with key allies instead of throwing them under the bus. At the U.N., she was widely respected by America’s friends and feared by its enemies. In the style of Thatcher, she called out dictators and tyrants from Beijing to Tehran. She rejected the poisonous appeasement mindset that dominates the White House today under the Biden administration.

Mrs. Haley is arguably America’s most prominent female conservative leader. One day she could be America’s first female president. Her views matter, especially at a time when the United States is under the thumb of the most left-wing presidency in U.S. history, one that is driving a big-government, high-tax and highly reckless agenda that threatens to saddle Americans with trillions of dollars of additional debt.

The world’s superpower, reeling from the national humiliation of the disastrous Afghanistan withdrawal, is also dangerously flirting with socialism at home, while its standing on the world stage has never been lower in the modern era. With good reason, Mr. Biden’s popularity is plummeting in the polls, and Americans are increasingly unhappy with the trajectory their country is taking.

This is a nation in crisis, with eroding self-confidence, declining economic freedom, and towering levels of public spending that will saddle future generations with an immense burden that could eventually bankrupt the world’s biggest economy. U.S. voters are already making their displeasure known with the Biden presidency. In the race for governor of Virginia, the Republican candidate, Glenn Youngkin, spectacularly defeated his Democratic rival Terry McAuliffe in a state that Mr. Biden won by 10 percentage points in the 2020 presidential election.

American conservatives like Mrs. Haley are drawing inspiration from Thatcher’s example in how she took on the socialist left and won, turning Britain around from the sick man of Europe into an economic power. Like her illustrious predecessor, Winston Churchill, Thatcher is hugely admired across the Atlantic and revered by practically every right of center leader in the United States, from former Vice President Mike Pence to Texas Sen. Ted Cruz. Her star has risen even further among American conservatives in the past few years. Memorably, in a visit to London as Secretary of State during the Trump Administration, Mike Pompeo invoked the spirit of Thatcher in urging the free world to stand up to China.

>>> The Margaret Thatcher Freedom Lecture

Americans remember the grit and determination of the greengrocer’s daughter from a humble background who, like Ronald Reagan in the United States, defied all the odds to lead a once-dominant world power that had simply lost the will to succeed and was in a state of self-loathing and catharsis. Both Thatcher and Reagan shared an optimistic vision of revival and renewal centered upon reining in the state’s power, getting big government off the backs of the people and advancing free-market policies that generated prosperity and reignited the entrepreneurial heart of both counties.

Britain’s present government, which is de facto the most powerful conservative administration in the world today, could learn from the embrace of Thatcherism by its counterparts on the American right. Raising taxes and expanding the state’s role will not benefit the British economy. It will hobble it and ultimately reduce Britain’s competitiveness at a time when it needs it most, in the new Brexit era freed of the shackles of the European Union.

Thatcher would have greatly cheered the vote to leave the EU but have strongly opposed any policies that undermined the U.K.’s ability to thrive and prosper as a truly free sovereign nation. As Mrs. Haley remarked in her Heritage lecture, “We could use some of Thatcher’s steely confidence and moral conviction” and embrace the Iron Lady’s vision of economic freedom and liberty.

Wise words the British prime minister should heed.