Prime Minister Sunank’s cabinet reshuffle comes straight out of right field — or left, depending on one’s view of the true political colors of the premier, under whose shaky leadership Britain’s Tories are taking a drubbing in the polls.

The surprise cabinet reshuffle Monday that saw Mr. Sunak appoint a failed prime minister, David Cameron, to the post of foreign secretary while sacking the home secretary, Suella Braverman, was followed by a scathing letter that Ms. Braverman sent to her now former boss. Also, she posted it to X. 

Little doubt obtains that the letter was less one of complaint than a move on Ms. Braverman’s part to toss her hat into the ring to lead the Conservative party. As London’s Daily Telegraph put it, the former home secretary “is not just exacting her revenge on Rishi Sunak but positioning to take over the Tories if they lose in 2024.”

The seeds of discord between Mr. Sunak and Ms. Braverman were long in the planting. In September, she delivered a speech at Washington in which she expressed her views on illegal immigration. Fast-forward to last weekend, following a series of controversial remarks she made in an article in the Times of London that included referring to pro-Palestinian protesters as “hate marchers” along with a claim that the police “play favorites” with protesters. 

In London’s current climate of political correctness, it seemed that Ms. Braverman’s days as Downing Street’s doyenne of all things interior were numbered. That was so even though a prominent Tory backbencher, Jacob Rees-Mogg, stated that Ms. Braverman only said what many people were thinking, calling her firing “a mistake, because Suella understood what the British voter thought and was trying to do something about it.”

Mr. Sunak had been under growing pressure to dismiss the 43-year-old Ms. Braverman — seen as a Tory hardliner — from one of the most senior jobs in government, responsible for handling immigration and policing. His decisions to fire her and appoint Mr. Cameron to a key post could easily backfire — to judge by Mr. Rees-Mogg’s reaction, party tensions are anything but soothed.  

Even if the prime minister’s maneuver ends up winning back centrist voters dismayed by the party’s swerve to the right on some issues, he also courts a real risk of alienating the Brexit-backing working-class voters who switched support to the Conservatives from Labor during the United Kingdom’s more recent national election in 2019.

Ms. Braverman, for her part, is clearly not throwing in the tea towel. The better part of her letter could be construed as throwing darts at Mr. Sunak, who appointed her as home secretary in October 2022. She wrote that she accepted that offer “despite you having been rejected by a majority of party members during the summer leadership contest and thus having no personal mandate to be prime minister.”

She wrote, too, that despite having sent numerous letters to the prime minister on key subjects in her remit, migration among them,  Mr. Sunak “manifestly and repeatedly” failed to deliver on every one of these key policies. She continued, “Either your distinctive style of government means you are incapable of doing so. Or, as I must surely conclude now, you never had any intention of keeping your promises.”

The clearest sign of staking out her claim for potential future stewardship of the Tories was this black pearl: “Someone needs to be honest: your plan is not working, we have endured record election defeats, your resets have failed and we are running out of time. You need to change course urgently.”

One of the specific subjects of which Ms. Braverman warned Mr. Sunak is the fate of the proposed Rwanda asylum policy, which the government has promoted as a lever to tackle the issue of small boats full of migrants landing on British shores. A former prime minister, Boris Johnson, first floated the proposal in April 2022 and it has faced legal challenges since. 

In her letter, Ms. Braverman admonished Mr. Sunak by writing, “If we lose in the Supreme Court, an outcome that I have consistently argued we must be prepared for, you will have wasted a year and an Act of Parliament, only to arrive back at square one.”

On Wednesday, Britain’s supreme court ruled the asylum policy to be unlawful. Whether that means Ms. Braverman will have the last laugh is too soon to tell. If Mr. Sunak thought he could relieve one headache by giving Ms. Braverman the heave-ho, though, Wednesday’s legal setback, which she predicted, might leave him reaching for the nearest bottle of aspirin.