In calling a general election, Prime Minister Rishi Sunak of Britain cast himself this week as a leader with a clear plan. That did not include carrying an umbrella during his remarks in front of 10 Downing Street, where Mr. Sunak was drenched in a spring shower that yielded a flood of snarky headlines.

“Drowning Street,” said the tabloid City A.M. “Drown & out,” cried The Daily Mirror. “Things can only get wetter,” declared The Daily Telegraph.

On Thursday, the first day of the six-week campaign, that dissonance spread from symbolism to substance. Mr. Sunak signaled that his government’s signature political project — putting asylum seekers on one-way flights to Rwanda — would not be set in motion before voters went to the polls on July 4.

Speaking to the BBC, Mr. Sunak cited the Rwanda policy to draw a sharp contrast with the opposition Labour Party, which he accused of having no plan to stop asylum seekers who make hazardous crossings of the English Channel in small boats.

“That’s the choice in this election,” the prime minister said.

But when he was asked if the first deportation flight would now take off after the election, he said yes, adding, “If I’m re-elected.”

To analysts and opposition leaders, Mr. Sunak’s admission foretold the end of a policy on which he may have spent more political capital than any other. Since the government first introduced the idea of sending asylum seekers to Rwanda in 2022, it has endured repeated legal challenges, fierce criticism from human rights groups and weeks of bitter debate in Parliament.