2: Parliament’s Nuclear Option

If they fail to legislate against a no-deal Brexit, lawmakers can resort to the ultimate weapon: a motion of no confidence, ousting Mr. Johnson from office. Currently, they do not appear to have the votes to make this happen. But even if they did, it might not solve the problem.

The law calls for the formation of a new government within two weeks or a general election. One option might be a caretaker administration that would presumably request another Brexit delay to afford time to hold an election. The problem is opposition leaders cannot agree on a caretaker prime minister. Jeremy Corbyn, the natural choice as leader of the Labour Party, is too left-wing, and as a lifelong critic of the European Union, is distrusted by determined opponents of Brexit.

Many would prefer a more centrist figure — perhaps the former Conservative cabinet minister Kenneth Clarke — as the caretaker. That would require Mr. Corbyn agreeing to stand aside, because a no-confidence motion could not succeed without his support.

And even if it did, Mr. Johnson has another trick up his sleeve, one that his supporters have repeatedly telegraphed: He could refuse to resign and then schedule a general election for November, in effect forcing through a no-deal Brexit. Dirty pool, perhaps, it would leave deep scars in the body politic. But there is nothing in the relevant law, the Fixed-Term Parliaments Act, requiring the prime minister to step down immediately.