LONDON—Theresa May has spent her entire time as prime minister trying to achieve one thing: Negotiating a Brexit deal that a majority of British lawmakers could support in order to give the U.K. the smoothest possible exit from the European Union at the end of March this year.

Tonight, the sum total of over two years of work was resoundingly rejected with the single biggest defeat of a sitting government in British history. Only 202 Members of Parliament voted for the deal, with 432 against.

The previous record defeat by 166 MPs, set in 1924, was shattered.

May is no stranger to crises. Of the scant areas of praise she’s received as prime minister almost all of it has been for her Terminator-like ability to carry on through a hurricane of setbacks, betrayals, and ridicule, most of it from within her own Conservative party.

But this vote was the big one—it had been named the “meaningful vote”—and the result has proved once and for all she cannot carry out the one job she was placed in power to do. With her deal so overwhelmingly defeated, May has failed, and the U.K. is on the brink of crashing out of the EU with no deal in place.

One Conservative MP admitted to The Daily Beast: “Honestly, not a fucking clue what happens next.”

Professor Robert Hazell, professor of government and the constitution at University College London, said this was Britain’s worst constitutional crisis for more than a century.

“A prime minister who suffered such a catastrophic defeat would usually be expected to resign, or advise the Queen to dissolve Parliament, triggering a general election,” he said. “The last time Britain faced a constitutional crisis on this scale was in 1910.”

The upshot in 1910 was an unprecedented two general elections held in the same year.

May is now forced to set out her next step within the next three days, with each option being one likely to undermine her even further. She can go back to the EU and beg for more concessions to persuade more lawmakers to back her deal in another vote; risk the economic catastrophe of no deal; or roll the dice and call for another referendum to let the British public decide whether or not her deal lives up to what they voted for in 2016.

That’s if she even gets a chance to attempt any of those options. The opposition party, Labour, responded to the vote by calling for a formal vote of no confidence in the government. If successful, May would be forced into a general election with both her reputation and the reputation of her party severely tarnished in the eyes of voters.

Labour insiders believe their best hope of winning a vote of no confidence lies with Northern Ireland’s DUP party, which agreed to prop up the Conservative government after it failed to secure an overall majority in the last election. The Ulster politicians have been appalled by May’s negotiating prowess and incensed by her repeated failures to include them in the process—on several occasions the prime minister has presented them with the results of her European negotiations as a fait accompli without securing their buy in.

If May signals any willingness to soften Brexit in order to win over potential support for her deal from the Labour benches, the DUP could be willing to pull the ripcord and bring this government to an end. For now, however, the DUP has pledged to stand by May in Wednesday’s vote of no confidence.

Assuming May survives the vote, there were signs on Tuesday evening that her Plan B would be to have another go at Plan A. That would entail her bringing back a slightly improved version of the deal to the Commons in the hope that MPs were so scared of a no-deal Brexit that they backed down and accepted that her compromise was the best they are going to get.

If a deal can’t win the support of a majority of lawmakers by the end of March, and May doesn’t attempt to extend or abandon the deadline of the exit, Britain would crash out of the EU with no deal in place. Such a scenario which would see the British economy shrink by 9.3 percent, according to the British government’s own analysis.

A cadre of hardcore Brexiteers will never accept a compromise deal and have continued to insist that plunging out of the European Union with no trade deals or continuity of service with EU institutions would in fact represent a “clean Brexit.”

Peter Bone, of the hardline pro-Brexit faction within the Conservative Party known as the ERG, said there is no point going back to Brussels looking for a few more concessions. “I think she needs to listen to what Parliament has said and accept her deal is dead,” he told The Daily Beast.

If May is unable to secure the support of rebels in her own party, the only way out of the mess would be to win over Labour politicians—some of whom have already indicated that they might be willing to support a deal negotiated by May because they believe they should enact the result of the 2016 referendum and because they believe a no-deal Brexit would be catastrophic.

One of Corbyn’s close allies on the Left of the party, Chris Williamson, told The Daily Beast that he was confident May would not be able to peel off enough of his Labour parliamentary colleagues to secure a majority for her deal no matter how many times she brought it back.

“I am absolutely sure of that,” he said.

May’s place in history will be defined by her ability to get this deal through. She suffered a hammer blow to her chances of that happening on Tuesday, but there is little sign of sympathy—even on her own side.

Nick Boles, a former Conservative minister, told The Daily Beast that she only had herself to blame. “From the very start of her premiership she should have reached out to MPs from other political parties and sought to craft a compromise deal that reflected the narrowness of the referendum result and that a majority of MPs could support,” he said. “Instead, she laid down a series of red lines at the behest or the small group of hardline Brexiteers and alienated almost all opposition MPs and many in her own party. The calamity that is about befall her is almost entirely of her own making.”