Could British voters reverse themselves as well? By Monday, four days after the Brexit vote, an online petition calling for a do-over had 3.8 million signatures.

But there is little reason to believe that a second referendum, were it held today, would yield a different result. While a handful of Britons have said on social media that they regretted their vote to leave the union, polling suggests that they are a tiny minority. A survey by ComRes, taken on Saturday, found that only 1 percent of “Leave” voters were unhappy with the results. (Brexit won by four percentage points, 52 to 48.)

British leaders could justify a second cut at the question by securing special concessions from the European Union, like allowing Britain to put a cap on immigration. This approach was how Danish and Irish leaders persuaded their voters to approve the referendums they had previously rejected.

Mr. Johnson, who said on Monday that Britain was “part of Europe and always will be,” hinted before the vote that he might pursue this strategy. “There is only one way to get the change we need, and that is to vote to go,” he wrote in a March op-ed in The Telegraph. “All E.U. history shows that they only really listen to a population when it says No.”

A second vote would allow politicians to claim that they had followed the will of the voters and stood up to the European Union, avoiding both populist outrage and the economic and diplomatic fallout of a British exit.

European leaders, however, may not be eager to go along. If any member state can extract special concessions by threatening to leave, it undermines the union’s ability to make Europe-wide policies. It also gives other states an incentive to play chicken with exit referendums, a dangerous game that could easily end in disaster.

There is also a risk that British voters would reject the second referendum as well. If that happened, there would truly be no going back.