Britain's Top Brexit Negotiator Raab Resigns, Dealing Blow to Theresa May

His resignation comes just hours after May won the support of her bitterly divided Cabinet for a draft deal to leave the EU after months of stalled talks and setbacks that have threatened the messy divorce known as Brexit as well as May's leadership.

But May had to make big concessions to the EU to achieve the deal. Britain, for example, will remain tied to the bloc's customs union for a transition period. The deal also prevents a "hard border" returning between EU member Ireland and Northern Ireland, which is part of the United Kingdom and has helped ensure peace there, USA Today reported.

In his resignation letter, Raab, Britain's Brexit secretary, said he could not "in good conscience" support the deal because it "presents a very real threat to the integrity of the United Kingdom." The British pound fell 1% against the dollar on the news.

Britain's Work and Pensions Secretary Ether McVey also resigned over the draft deal, as did several parliamentary aides and a junior minister for Northern Ireland.

May is already facing an uphill struggle to convince enough lawmakers in Parliament to accept the agreement with the EU before it is scheduled to depart the bloc in March.

Britain's leader secured the backing of her Cabinet for the deal after an "impassioned" five-hour debate on Wednesday. "I firmly believe, with my head and my heart that this is a decision which is in the best interests of the United Kingdom," she said, referring to the support from her Cabinet as a "collective agreement."

Addressing lawmakers on Thursday, May insisted that she had taken "the right choices, not the easy ones" on Brexit.

Yet while securing Cabinet approval was an important step for May, the deal still needs approval from the EU at a summit in the next few weeks. Then May will need to win backing from Britain's Parliament, where pro-Brexit and pro-EU legislators alike are threatening to oppose it. Thursday's Cabinet-level resignations add to the pressure and British media have suggested that a move to oust May from power is conceivable.

Pro-Brexit lawmakers in May’s divided Conservative Party are angry over the draft agreement because they believe it will leave Britain tethered to the EU after it departs the bloc. "I cannot reconcile the terms of the proposed deal with the promises we made," Raab said in his resignation letter.

McVey, the jobs minister, said in her letter it is "no good trying to pretend to (voters) this deal honors the result of the referendum when it is obvious to everyone that it doesn’t."

Britain voted to leave the EU by 52 percent to 48 percent in the vote. Some polling data indicate that if there were a second Brexit vote a majority would chose to stay in the EU. May has repeatedly rejected the idea of holding a second vote.

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