Today marks a Brexit milestone. Alongside the June 2016 referendum and the Prime Minister’s Lancaster House speech of January 2017 will stand Boris Johnson’s personal statement to the House of Commons. It has one theme: “It is not too late to save Brexit.”

Doubtless this is the opening salvo of more challenges to come, for which Mr. Johnson now leads the pack. In other words, while it may not be too late to save Brexit, it may be too late to save Theresa May’s leadership of the Conservative Party.

Mr. Johnson’s resignation last week as foreign secretary came three days after Mrs. May’s Cabinet summit Friday at the premier’s official country seat, Chequers. She capitulated to the European Union and betrayed the promise of Brexit.

Boris Johnson. (Image source: Chatham House/Flickr)

The subsequent white paper outlining the government’s formal position only added insult to injury as the full extent of her opening round of appeasement became known. “In important ways this is BINO or Brino or Brexit in name only,” Mr. Johnson told the House, adding that he was “of course unable to support it.”

Mr. Johnson’s verbal shot mightn’t be heard round the world, but it was a shot across the Prime Minister’s bow with advice that she “can fix that vision once again before us” and “deliver a great Brexit for Britain” to “unite this party, unite this House, and unite the country.”

Time, though, grows short. The initial referendum euphoria of Britain realizing its own Independence Day was soon obscured by “a fog of self-doubt.” Instead of riding high on the flooding tide of fortune, Mr. Johnson bemoaned, Britain “dithered” and “burned through negotiating capital.”

Now, Mr. Johnson said, “after 18 months of stealthy retreat,” Britain had come “from the bright certainties” of Lancaster House, where Mrs. May outlined her goals and negotiating strategy, to the Chequers agreement, where she upended them.

Mr. Johnson ticked off each step of the descent. From Lancaster’s promise of Westminster-made rules comes Chequers’ offer of “harmonization” with a common EU rulebook. From a promise to regain sovereignty and become rule-makers comes the offer to remain rule-takers.

And from the promise that Britain would throw off the yoke of EU regulatory dominance so that Brexit means Brexit, comes the offer to abide by the Brussels bureaucracy and submit to its adjudication process. Said Mr. Johnson: “We are volunteering for economic vassalage.”

Nor was Mr. Johnson solely addressing the House of Commons, and in particular his Conservative colleagues. He spoke to Brexiteers across the United Kingdom who are aghast at how the Leave negotiations have stumbled into mayhem.

“We continue to make the fatal mistake of underestimating the intelligence of the public,” Mr. Johnson warned his fellow parliamentarians, “saying one thing to the EU about what we are doing, and then saying another thing to the electorate.”

Mr. Johnson’s partisans know that recent polling shows that Britons don’t believe that Mrs. May will meet her Brexit obligations, that fed-up Conservative voters are shifting to the United Kingdom Independence party, and that the Labor opposition enjoys more support than the minority Tory government.

Nor has it been lost on Fleet Street that Mr. Johnson stood near to where another former foreign secretary, Geoffrey Howe, gave his resignation speech in November 1990. That turned out to mark the beginning of the end of Britain’s first female prime minister, Margaret Thatcher.

Even political adversaries will admit Boris Johnson’s ability to turn a phrase with rhetorical flourish. Once more he obliged. “Let us again aim explicitly for that glorious vision of Lancaster House, a strong independent self-governing Britain that is genuinely open to the world, not the miserable permanent limbo of Chequers,” Mr. Johnson exclaimed.

And he offered parting counsel. “We need to take one decision now before all others – and that is to believe in this country and in what it can do.” Brexit’s far-flung friends are “fully expecting us to do what we said and to take back control.”

Here the ex-foreign minister invited his listeners to cast their imaginations back to the British hey-day of innovation and competitiveness that marked the zenith of its industrial revolution, and to once more “do proper free trade deals for the benefit and prosperity of the British people.”

Among Britain’s global friends is Mr. Brexit himself, President Trump, who, in an unusual break from protocol, cautioned Mrs. May that her Chequers agreement embedding British commerce within the EU framework would make a future deal with America less probable.

“That was the vision of Brexit we fought for,” Mr. Johnson exhorted the Commons. “That is the prize that is still attainable.” Has the British government the wisdom, the humility, and the fortitude to steer away from its Chequers folly and heed its sandy-haired harbinger of hope? Or does the fate of Brexit hang on the slogan “BoJo for PM”?