Part of the problem is sheer complexity. There will be 10 parallel tracks of negotiations involving a team of 100 on the British side alone. The first round will run from Monday to Thursday of next week in Brussels, with the teams reconvening in London on March 18. At that rate, there will be time for only half a dozen rounds before Britain takes stock of the progress.
Moreover, some of the early sticking points — like the European Union’s access to British fishing grounds — are going to be the most contentious. There is also growing tension over whether Mr. Johnson is quietly reneging on the status of Northern Ireland in the withdrawal agreement.
British officials say there will be no need for checks of goods flowing from Britain to Northern Ireland since Northern Ireland remains part of the British customs territory. But under the terms of the agreement with Brussels, the North will also adhere to European Union regulations. This hybrid status, experts say, makes it impossible for there to be no border checks.
Adding to the fears of a bitter negotiation, Mr. Johnson reshuffled his cabinet to stack it with hard-line Brexiteers. He replaced the Northern Ireland secretary, Julian Smith, who almost quit last year when Mr. Johnson threatened a no-deal Brexit, with Brandon Lewis, who is viewed as more compliant.
Sajid Javid, the chancellor of the Exchequer who voted to stay in the European Union in 2016, was forced out in a power struggle with 10 Downing Street. Analysts say that his successor, Rishi Sunak, is likely to put up less resistance to a confrontation with Brussels.
Some analysts chalk up the fighting words to an opening gambit. Britain and the European Union, they say, both have a strong incentive to come to terms. During the withdrawal talks with Brussels, Mr. Johnson showed an ability to pivot seamlessly from confrontation to compromise.
Yet other experts note that Mr. Johnson’s ultimate motives remain something of a mystery. He has yet to speak in detail about what kind of Brexit he wants. Some note that the disruption of failing to make a deal, while indisputably bad, would not be magnitudes worse than the bare-bones deal that Mr. Johnson says, for now, that he is seeking.