Prime Minister Boris Johnson will find out Tuesday evening whether he can muster a majority in the House of Commons to support his Brexit deal.
Even if he does, it may not be enough to get the agreement through Parliament by his October 31 deadline.
Having twice been denied a vote on whether lawmakers support his deal, Johnson has introduced the Withdrawal Agreement Bill, which would implement the deal in law, and plans to push it through Parliament at a breakneck pace.
His moment of truth will come on Tuesday evening in London, with what's known as the Second Reading vote - on whether Parliament agrees with the general principles of the bill.
He needs to persuade 61 Members of Parliament to back his deal. It looks like he has 64, based on what lawmakers have said over the last week. Here's our tally of how many look like they will support his deal:
However, his plan to fast-track the legislation through Parliament is more controversial. Even lawmakers who support his deal have expressed concern about the lack of time it provides for proper scrutiny. If he doesn't pass that hurdle, he could still deliver Brexit - just not in time for his deadline.
Here's how the numbers break down:
The last time Theresa May tried to get her deal through, in March, she had the support of 279 Conservatives. They are mostly likely to back a Johnson deal too, but there are some problems.
That leaves Johnson 61 votes short. Where can he go?
In Saturday's vote, seven of the Gaukeward Squad went against Johnson, but almost all made it clear they were ready to back his deal. Former Chancellor of the Exchequer Philip Hammond still seems uncertain, but Johnson seems to have the vast bulk with him.
They seem to have failed in their efforts to persuade Tories to vote against the deal, but on Saturday, they inflicted defeat on Johnson by voting against him, and they look ready to do it again.
When Johnson became prime minister, the Spartans were adamant they opposed anything but the most minimal Brexit agreement. But in recent weeks they have begun to see the virtues of compromise. This is the result of the Benn Act, legislation that aims to prevent the UK leaving on Oct. 31 unless Johnson has reached a deal. It's made the Spartans fear losing Brexit altogether.
May pinned her hopes on winning the support of a significant minority of MPs from the opposition Labour Party who believe the 2016 referendum result must be honored. She struggled to get more than five to vote with her, but 15 who didn't back her last time joined some who did in signing a letter this month urging the EU to do a deal. That might imply a commitment to vote for such an agreement.
Four independent MPs backed May's deal in March. A fifth, John Woodcock, might also be tempted. He voted with Johnson on Saturday. But Sylvia Hermon, who backed May's deal, represents a Northern Irish seat and is opposed to Johnson's deal.