But London projected a different image of the Brexit talks, with Britain’s prime minister, Boris Johnson, describing the goal as being “shrouded in mist.”

The conflicting signals reflected the complexity and sensitivity of the negotiations, and the fact that neither side wants to be blamed should the talks collapse … again.

Mr. Johnson spent much of Wednesday trying to rally 10 lawmakers from Northern Ireland’s Democratic Unionist Party, who worry about what a post-Brexit border with Ireland would look like.

What’s next? E.U. leaders will gather at a summit today. If they approve some kind of a deal, Mr. Johnson will then try to ram it through Britain’s Parliament on Saturday — a deadline imposed by British law that, if missed, would require the prime minister to push Brexit beyond Oct. 31.