LONDON -- The morning after the night before was a rough one for British Prime Minister Theresa May. On Wednesday night, she announced that she'd won her cabinet's backing for her draft proposal on how the U.K. should pull out of the European Union. On Thursday morning, May's Brexit secretary, the man who led her negotiating team in Brussels to hammer out that draft, quit, along with another member of her cabinet and several junior ministers.

Dominic Raab, the second of May's Brexit secretaries to quit the role in as many years, said the draft agreement reached with Brussels would effectively leave Britain beholden to the rules and regulations of the European Union and even give the EU the power to stop the U.K. from extricating itself down the road. He said he could not "in good conscious support the terms" of the deal he helped to craft.

Raab wasn't the only member of May's government to walk out on Thursday. Her Work and Pensions Secretary Esther McVey, Junior Northern Ireland minister Shailesh Vara, junior Brexit minister Suella Braverman, and parliamentary private secretary Anne-Marie Trevelyan also stepped down.

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All indicated that they could not support the almost-600-page draft deal May presented on Wednesday, which is considered insufficient by both Brexit backers and those who wanted to remain in the EU.

The prime minister's team made some major concessions to the EU to achieve the draft deal: Britain, for example, would remain tied to the European Union's customs union -- subject to it's collective trading rules and tariffs -- during a transition period, and potentially for much longer.

Raab said the agreement was unacceptable, and he could not support the so-called "back-stop" agreement in the draft, under which he said "the EU holds a veto over our ability to exit" the union.

"No democratic nation has ever signed up to be bound by such an extensive regime, imposed externally without any democratic control over the laws to be applied, nor the ability to decide to exit the arrangement," Raab said.

"I believe with every fiber of my being that the course I have set out is the right one for our country and all our people," May said at a press conference late Thursday.

What happens next?

As pro-Brexit Conservatives called for a no-confidence vote in their leader, a defiant May insisted Brexit meant making "the right choices, not the easy ones" and urged lawmakers to support the deal "in the national interest."

"Am I going to see this through? Yes." May told reporters late Thursday.

But the resignations, less than a day after the Cabinet collectively backed the draft divorce agreement, weakened May and emboldened her rivals within her Conservative Party.

Parliament still needs to approve the deal and it is unclear whether May has the numbers to push it through, or whether she can even remain in office long enough to bring it to a vote.

With the ministers on Thursday joining 10 others who have resigned from May's government over the last year, talk of a challenge to her leadership was growing louder.

One of her most vocal opponents within the Conservative Party, leading hardline "Brexiteer" Jacob Rees-Mogg, ripped May on the floor of Britain's Parliament on Thursday over the draft, which he said failed to deliver on the party's promise to pull the U.K. out of the EU.

He said May's words and actions "no longer match," and confirmed that he had filed a letter of "no confidence" in the prime minister as the leader of the party.

If 15 members of May's Conservative Party submit letters of no confidence in her, it will trigger an internal leadership election in the party, and if she is toppled in that race she would be forced to stand down as British Prime Minister.

"I cannot overstate the seriousness of the situation the prime minister now finds herself in," the opposition Labour Party's Shadow Brexit Secretary Keir Starmer told BBC News on Thursday. He said "now there will be very serious attention to, 'what are the other alternatives.'"

Talk off another public vote

"All options need to be on the table, and that includes of option of campaigning for another vote," Starmer said, alluding to a growing movement in the U.K. public, and among lawmakers from all parties, for another public referendum on any Brexit proposal eventually finalized by parliament.

Calls are mounting -- and fast, after May herself appeared to indicate on Wednesday night that Brexit wasn't inevitable -- for any hypothetical second referendum to include a "no Brexit" option.

After months saying the choice facing Britain was either accept her deal with the EU, or crash out of the Union on March 29 with a "no-deal" Brexit, May admitted Wednesday that it was still possible the U.K. could remain in the union, in spite of her vows to uphold the will of the public which voted in 2016 to leave it.

She argued on Thursday that her draft agreement with the EU represented, "the right choices, not the easy ones."

May was adamant that her government was not planning for any contingency that did not include a British exit of the European Union.

Pound hit hard by Brexit chaos

The British pound fell sharply on Thurday after Raab announced his resignation from the government.

The currency dropped 1 percent, a relatively large decline for an established currency, to $1.2870 within minutes of Raab's tweet announcing he could not support the proposal.