Boris Johnson's task of assembling the 320 votes he needs to win a majority for his Brexit deal at Westminster on Saturday is complicated by the fact he is wooing three groups with diverging interests.
To reach a majority, he must win over almost all of the 28 Conservative Brexiteers who voted against Theresa May's deal three times, most of the 21 former Conservatives he expelled from the party last month and many of the 19 Labour MPs who have said they want to vote for a Brexit deal.
His problem is that the arguments employed to win over one group can alienate another, as he discovered when Brexiteer John Baron outlined an assurance he had received from the prime minister's allies.
"Because provided we can get that clear assurance, and I have been given it so far by people like Michael Gove and Dominic Raab, and I'm hoping to get it from the prime minister tomorrow, that we will be leaving after the trade talks, if those trade talks fail up to December 2020, on no-deal terms – as long as we can get that assurance, and I think we have done, then we'll be supporting the deal tomorrow," he told the BBC.
Baron's statement set off alarms among the expelled Conservatives, including former chancellor of the exchequer Philip Hammond, who fear that the deal could simply have the effect of postponing a no-deal Brexit by a year. It could also deter wavering Labour MPs who need confidence that the Brexit deal will not lead to lower employment and environmental standards.
The vote could be complicated further if House of Commons speaker John Bercow accepts an amendment from Oliver Letwin that would strip it of much of its authority. The amendment would mean that the Commons would not be deemed to have approved the deal until all implementing legislation was passed. And it would mean that the prime minister would have to request a three-month delay to Brexit under the Benn Act even if he wins the vote.
Johnson appears to have won over most of the Conservative Brexiteers but some still have questions and will not decide how to vote until Saturday morning. Others could be swayed by the arguments of the DUP's Sammy Wilson and Ian Paisley, who have been reminding them of their steadfast support for Brexit and warning about the deal's impact on the integrity of the United Kingdom.
The outcome is likely to hang on the votes of a handful of MPs and the prime minister’s own performance in the chamber – and the arguments made by speakers during the debate could prove decisive.