On Friday morning, Boris Johnson had a spring in his step.
He'd returned from Brussels with a new Brexit withdrawal deal. Most of his own party supports it, and although Northern Ireland's Democratic Unionist Party is withholding support, opposition lawmakers were lining up behind the deal.
Johnson was making clear to these supporters of a softer Brexit that if they don't vote for his deal, then they make a no-deal crash out a real possibility. And for some hours, Johnson's "my deal or no deal" gambit was working.
Then Oliver Letwin published his amendment, killing Johnson's momentum.
The Letwin amendment essentially means that the government cannot pass the deal in full until all of the Brexit legislation has passed. Letwin says that his aim is to provide a safety net to avoid an accidental no deal.
The government thinks that it's a plot to delay Brexit and prevent the UK from leaving the EU. They might have a point. Johnson is obliged by law to request a Brexit extension if no formal deal is agreed by the House of Commons at 11 p.m. tonight. The Letwin amendment effectively makes meeting that requirement impossible.
Letwin has presented MPs with an alternative to the "my deal or no deal" threat issued by Johnson and the government. And for now, it's killed dead the rush of support for the Prime Minister.