Theresa May's draft Brexit plan isn't dead yet - but its chances of survival certainly aren't looking good. With only 10 days until a hoped-for EU summit, the government of Theresa May lost a key senior official Thursday morning when Brexit Secretary Dominic Raab, the senior cabinet official who would have been responsible for selling the plan to the House of Commons, tendered his resignation, saying he could not in good faith support May's draft plan. In his resignation letter, Raab (the second Brexit secretary to quit May's government in the past six months) said he couldn't support the deal for two reasons: Its treatment of Northern Ireland would be a "very real" threat to the integrity of the UK, and the indefinite backstop would effectively grant the EU veto power over when the UK could leave. Today, I have resigned as Brexit Secretary. I cannot in good conscience support the terms proposed for our deal with the EU. Here is my letter to the PM explaining my reasons, and my enduring respect for her. pic.twitter.com/tf5CUZnnUz — Dominic Raab (@DominicRaab) https://twitter.com/DominicRaab/status/1062992019449098241?ref_src=twsrc%5Etfw!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0],p=/^http:/.test(d.location)?'http':'https';if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src=p+"://platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); Raab's resignation doesn't necessarily mean that May is toast - he said in his letter that his respect for the leader "remains undimmed." But signs that Raab's departure could trigger a cascade of resignations have already emerged as, roughly an hour after news of Raab's resignation broke, Esther McVey, May's secretary of state for work and pensions, also resigned (though her departure from May's government was somewhat less surprising). Earlier this morning I informed the Prime Minister I was resigning from her Cabinet pic.twitter.com/ZeBkL5n2xH — Esther McVey (@EstherMcVey1) https://twitter.com/EstherMcVey1/status/1063008263225126912?ref_src=twsrc%5Etfw!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0],p=/^http:/.test(d.location)?'http':'https';if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src=p+"://platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); With McVey gone, Bloomberg warned us to keep an eye out for more Cabinet dominoes: Penny Mordaunt, Andrea Leadsom and possibly Michael Gove, three senior ministers who have reportedly expressed doubts about the plan, could all resign, fearful of being outflanked. As frustrations with the deal grow, Conservative MP Anne Marie Morris told Sky News that she has submitted a letter of no confidence to the 1922 Committee. 48 letters would be needed for May to face a leadership challenge. May is expected to deliver a statement in response to the resignations, where she will reportedly insist that "nothing has changed." By resigning, McVey and Raab can now vote in Parliament against May's deal.