LONDON (NYTIMES) - Prime Minister Boris Johnson suffered a stinging defeat on Saturday (Oct 19) as Parliament rebuffed his campaign to take Britain out of the European Union by the end of the month and forced him to seek an extension that he had vowed never to pursue.

The turbulent events left Mr Johnson's agreement in limbo and threw British politics once again into chaos, with any number of outcomes possible: a no-deal exit from the EU, a second referendum on whether to leave at all, or a general election that could shift the balance in Parliament. The only sure result was continuing frustration and confusion among the British public.

Late on Saturday night, Mr Johnson formally applied to the EU, in an unsigned letter, for another extension of Britain's departure, something he said he would rather be "dead in a ditch" than do.

Mr Johnson sent a separate signed letter to the president of the European council, Mr Donald Tusk, in which he said a "further extension would damage the interests of the UK and our EU partners, and the relationship between us".

The conflicting letters left it to the EU to decide how to respond to Mr Johnson. Most analysts expected it would grant an extension, although that was unlikely to clarify the muddled situation in London.

It capped a dramatic day of legislative manoeuvring in which lawmakers debated Mr Johnson's deal while enormous crowds of anti-Brexit protesters marched outside Parliament,

Mr Johnson implored lawmakers to approve the agreement, which would pave the way for Britain to leave the EU at the end of the month.

The Prime Minister argued that it was the best deal Britain could hope to strike - one that, in his telling, would position the country for a thriving future as an agile free agent in the global economy - and that any further delay would be "pointless, expensive and deeply corrosive of public trust".

Instead, by a vote of 322-306, lawmakers passed a last-minute amendment, brought by Mr Oliver Letwin, an expelled member of Mr Johnson's Conservative Party, that would delay final approval on the agreement until after Parliament passes the detailed legislation to enact it.

A defiant Mr Johnson said he would push for another vote on his agreement early in the coming week. But that could present opponents with an opportunity to try to amend his plan.

"I'm not daunted or dismayed by this particular result," Mr Johnson said.

Still, it was a stinging setback for the Prime Minister - and as with his previous defeats in Parliament, one that came at the hands of a former member of his own party.

Mr Letwin, a veteran Conservative lawmaker, was purged from the party last month for supporting a law intended to prevent Britain from leaving the EU without any agreement, which many see as risking a disorderly, economically damaging rupture.

Mr Letwin, who supports Mr Johnson's Brexit deal, argued that the amendment was simply a safety net to prevent pro-Brexit hardliners from sabotaging the implementing legislation and, in the ensuing political vacuum before the Oct 31 deadline, engineering the no-deal rupture that some want.

Yet some opponents of Mr Johnson's Brexit deal supported the Letwin amendment, too - in hopes that further delays might open the door to other options.

For the Prime Minister, who has staked his claim to No. 10 Downing Street on delivering the withdrawal, the amendment was another in a series of setbacks in Parliament, preventing him from forcing lawmakers into a binary decision on whether to support his plan.

Assuming that Mr Johnson does request another Brexit extension, the EU would have to decide whether to grant a delay of a few more weeks to resolve the technical details or a longer delay to allow a general election or perhaps a second referendum.

Meeting on a Saturday for the first time since the Falklands War in 1982, members of the House of Commons rose, one after the other, to fervently endorse or reject Mr Johnson's deal.

The debate seemed to be ultimately less about the details of the plan, with its fiendishly complicated arrangements for trade with Northern Ireland, which is part of the United Kingdom, than about whether Britain could finally put Brexit behind it.

Opponents of the plan accused Mr Johnson of negotiating a shoddy deal that would leave a post-Brexit Britain vulnerable to predatory trade deals with other countries, not least the United States.

"This deal would inevitably lead to a Trump trade deal, forcing the UK to diverge from the highest standards and expose our families to chlorine-washed chicken and hormone-treated beef," said the leader of the opposition Labour Party, Mr Jeremy Corbyn, referring to fears of chemically treated imports from the US.

For Mr Johnson, 55, a flamboyant politician and former mayor of London who has been in office since July, it was a crucial moment.

He spoke with a tone of gravity and conciliation that contrasted starkly with the inflammatory language he has used during previous parliamentary debates over Brexit.

Mr Johnson's deal differs from those of his predecessor, Mrs Theresa May, primarily in its treatment of Northern Ireland.

Needing to avoid physical border checks, Mrs May opted to keep the entire UK in the EU's customs union, which was unacceptable to hardline Brexiters.

Mr Johnson sought to satisfy them by keeping Northern Ireland subject to the bloc's rules in a practical sense but legally outside it with the rest of Britain.

His deal is at the extreme end of divorce settlements that Britain could have negotiated with the EU.

It commits the country to very little alignment with the bloc on trade or regulations, turning its back on much of the web of rules that critics in Britain consider stifling or a threat to their sovereignty.

By keeping the EU at arm's length, Mr Johnson and his lieutenants contend, Britain can set out to transform itself into an agile, lightly regulated competitor in the global economy - or "Singapore-on-Thames", to use a phrase coined by Brexit evangelists.

To do that, however, Britain must first negotiate new trade agreements with dozens of parties, including the EU and the US, a painstaking process that could take several years.

And Mr Johnson's plan allows for only a transitional period ending in 14 months, although this could be extended for a maximum of two years.

The debate on Saturday came after more than three tumultuous years of division and discord over Brexit, an ordeal that has shaken British politics and tested traditional loyalties, both among lawmakers and voters.

In 2017, Mrs May called an election betting that she could persuade voters to give her a big majority in Parliament to negotiate a Brexit accord. That proved a fatal error when she lost her majority and with it, much of her authority within the governing Conservative Party.

Although she later succeeded in negotiating a Brexit deal, she failed three times to get it through the House of Commons and was ultimately forced to request two Brexit delays.

Even before that, her enemies were circling - not least Mr Johnson, who resigned from her Cabinet after complaining that her deal would make Britain a vassal state of the EU.

That helped feed a narrative that has polarised British politics, with many supporters of Brexit moving toward a more brutal rupture with the EU than its proponents suggested in the 2016 referendum.

At the same time, Brexit opponents became less inclined to settle on a compromise that they saw as the worst of both worlds. Voters increasingly came to identify themselves more as "leavers" or "remainers" than by traditional loyalty to any party.

Facing competition from the Brexit Party, led by Mr Nigel Farage, the Conservatives have now embraced a hardline form of exit, a transition that gained momentum last month with the purge of 21 Conservative rebels, including Mr Letwin.

The Labour Party still said it wants to negotiate a different, softer Brexit deal and would put that to a referendum, with remaining in the EU being the alternative.

The smaller and more pro-European Liberal Democrats said they would stay in the bloc without holding a second vote.

But while political sentiment has fled the centre ground, there is a growing sense of exhaustion among many voters about Parliament's endless haggling over Brexit.

That has proved a powerful weapon for Mr Johnson, who has argued that he would "get Brexit done" - even if the reality is that Britain's legal departure from the EU is only a stage in a much longer process.