May is prime minister. Practically this role is similar to president and majority leader combined. Essentially she is finally responsible for everything.

Unfortunately for her there are essentially three groups. (1) Brexit on WTO terms, (2) cancel Brexit and remain, and (3) those that largely support her deal. These groups are more certain what they don't want than what they do want. This means that 2/3 of the MPs oppose this deal. But 2/3 will oppose any option.