Sir Keir Starmer, Labour’s white knight, is stumbling out of the gate. On the clubhouse turn, a new poll shows him 16 points underwater, a plunge of 27 points from when he acceded to prime minister. His victory in the July 4 vote prompted an outpouring of eulogies for the Tories, who’d ruled Britain for 14 years. Labour earned its 411 seats, though, with just over 33 percent of the vote. That’s a far cry from proportional, and shaky stuff for a landslide.

Labour’s election slogan was “Change,” hardly a detailed agenda. Now, though, Britons appear to be assessing whether all change is good change. We viewed the rise of Sir Keir with caution, though we admired his commitment to eradicating from Labour the antisemitism that had, during the tenure of  Jeremy Corbyn, taken hold in the party to a shocking degree. Sir Keir’s effort helped to rehabilitate one of the storied political parties of the West.

No sooner did Sir Keir enter Downing Street, though, than a retreat began from that promise, with a hard left turn against Israel. The  foreign minister, David Lammy, has set himself against the Jewish state to such an extent that Prime Minister Netanyahu elected not to see him when Mr. Lammy visited Jerusalem. And with good reason — London has decided to drop its challenge to the International Criminal Courts’s prosecution of Mr. Netanyahu.

What a betrayal of the glorious promise of Sir Arthur Balfour’s bequest. It suggests that London will be an unreliable ally to Israel in wartime. Sir Keir’s troubles, though, are local as well as Levantine. Surveys report that most Britons oppose his plans to cut fuel payments for pensioners. That’s the kind of move that can quickly sour an electorate that just five years ago handed Prime Minister Johnson his own hefty mandate. 

On Thursday, the New York Times issued a lengthy dispatch in respect of “How the Tories Lost Britain.” They blame Prime Minister Truss’s  “ill-judged foray into Ronald Reagan-style, trickle-down tax cuts that frightened the financial markets” and reckon that “it is an overstatement to say that Brexit caused the Conservative crackup — but not by much.” Brexit is judged to be “political kryptonite.” 

What, though, of Mr. Johnson’s transformation from a Brexit Superman to a big government ersatz Labourite, promising to spend money that England didn’t have for policies that the country didn’t need. An attachment to the chimera of a green revolution — kryptonite-green — was the last thing that the country wanted from a Conservative government. The warnings are all there for Sir Keir. Landslides hardly preclude losses.

Most perilous of all for Sir Keir could be the riots that have roiled England after three young girls were murdered at a dance class at Southport. Our columnist Julie Burchill reports that for an inconsistent approach to law and order the prime minister is being called “Two-Tier Keir.” Ms. Burchill relates that more and more of her countrymen are “baffled by what has happened to their country, a country they no longer recognise.”

Therein lurks a warning for, among others, Vice President Harris. Like Sir Keir, she came of political age as a prosecutor. She is running on a platform of vagueness, convinced that merely being an alternative — to Presidents Biden and Trump, just as Sir Keir is to Mr. Corbyn and Prime Minister Sunak — is an achievement. It could work. Mr. Starmer’s example, though, is also a warning that leaders can lose a mandate and the issues will have their day.