The U.K. Labour Party’s Worst Enemy Might Be Itself

These days, the only thing that can stop the Labour Party, it seems, is the Labour Party.

For more than a year, the leader of Britain’s main opposition party, Keir Starmer, has sat on a double-digit lead in the polls over the Conservative Party. But a pair of embarrassing suspensions of Labour parliamentary candidates for their comments about Israel, a week after a messy reversal on climate policy, have thrown Mr. Starmer on the defensive, raising questions about his management skills and taking the spotlight off the long-suffering Conservatives.

“Keir has had a really good, long run but he’s not Man City,” said John McTernan, a political strategist, referring to the Manchester soccer club that is a perennial champion of Britain’s Premier League. “The question is, can he come back next week fighting?”

Labour still holds a double-digit lead over the Conservatives in polls. It could swiftly regain its stride with victories in two parliamentary by-elections on Thursday, both of which it is expected to win. And the Conservative Prime Minister Rishi Sunak has committed his share of missteps.

But Labour’s setbacks are a reminder that with a general election still at least a few months away, Mr. Starmer cannot take anything for granted.

Analysts said the party’s decision to mothball its flagship climate initiative was potentially damaging because it plays into a Conservative narrative that Labour does not stand for anything. It pulled the policy after a lengthy internal debate that leaked into the public, because the price tag — 28 billion pounds, or $35 billion, a year — seemed untenable, given Britain’s big rise in borrowing costs since the policy was first announced in 2021.

In the case of the candidates, Labour arguably compounded its problems by acting too slowly. It stuck by one of them, Azhar Ali, for almost two days after a London tabloid, The Mail on Sunday, reported that he had claimed Israel “allowed” the Hamas attack on Oct. 7, in which 1,200 civilians and soldiers were killed.

Labour eventually revoked its support for Mr. Ali, even at the cost of losing the seat in the constituency of Rochdale, north of Manchester, for which he is still running. But the episode revived allegations of lingering anti-Jewish sentiment in the party’s ranks, despite Mr. Starmer’s concerted — and by most accounts, successful — campaign to root out systemic antisemitism.

The outcry over Mr. Ali guaranteed that when another Labour candidate, Graham Jones, was accused on Tuesday of making anti-Israel remarks, the party quickly suspended him. Mr. Jones had been selected to compete in the general election for a seat he once held in Lancashire.

“I don’t think it symbolizes a great strand of anti-Semitism in the Labour Party,” said Jonathan Powell, who served as chief of staff to a former Labour prime minister, Tony Blair. Under Mr. Starmer, he noted, Labour has maintained a pro-Israel position during the Israel-Gaza war. That would have been inconceivable under his predecessor, Jeremy Corbyn, when Labour was a hotbed of anti-Israel fervor.

Still, Mr. Powell said the party could face a recurring problem if the pro-Tory press unearthed and published problematic statements on a variety of issues by other Labour candidates. “If you’re going to rule out candidates for seats for saying anything silly in their lives,” he said, “you’re not going to have many candidates.”

However successful Mr. Starmer’s campaign against anti-Semitism has been, the episode shows how vital it is for the party to conduct due diligence on candidates. By the time Labour cut loose Mr. Ali, it was too late to replace him on the ballot for the by-election, which is scheduled for Feb. 28. If he manages to win anyway, he will not sit in Parliament as a Labour lawmaker.

In a strange twist, Mr. Ali will run against two former Labour lawmakers: George Galloway, who was expelled from the party in 2003 because of his opposition to the Iraq war and represents the Workers Party of Great Britain; and Simon Danczuk, who was suspended by Labour for sending sexually explicit messages to a 17-year-old girl. He is the candidate of the right-wing Reform U.K. party.

The Israel-Gaza war has put Labour in a tricky position because — alongside its support for Israel, which it shares with the Conservative government — it wants to signal to voters in Muslim communities that it understands their anguish and outrage at the rising death toll among Palestinians.

Still, critics argued that the hesitation in abandoning Mr. Ali revealed a weakness in Mr. Starmer, a former public prosecutor who has not run a national campaign. Some pointed to the similarly dilatory debate over the future of Labour’s green policy, which analysts said became a tug of war between Mr. Starmer and the party’s fiscally conservative shadow chancellor of the Exchequer, Rachel Reeves.

“There is something in the operation that, when under pressure, seems to give a bit,” said Mr. McTernan, a onetime aide to Mr. Blair. “That is not an issue now because Labour is 20 points ahead in the polls. But it’s an issue to be sorted out now because in a general election, these things will happen once an hour, they won’t happen once a week.”

The drama over the green policy allowed the Conservatives to paint Labour as a party of U-turns and flip-flops. But Labour allies said that was a reasonable price to pay to avoid being tarred as fiscally irresponsible. Mr. Starmer and Ms. Reeves are determined to reassure voters that taxes will not rise under Labour and that the party can be trusted with the public finances.

“There are some really serious considerations about the country’s fiscal position, Labour’s policy priorities, and how they match what they want to do in government with the reality they are going to face,” said Claire Ainsley, a former policy director for Mr. Starmer.

“I am not surprised if that took some weeks, if not months, for there to be proper conversations,” said Ms. Ainsley, who now works in Britain for the Progressive Policy Institute, a Washington-based research institute.

Some of Labour’s troubles, analysts said, are merely a function of having held a lead in the polls for so long that the British press now treats the party as a government in waiting. That means, among other things, that journalists subject Labour to closer scrutiny than an ordinary opposition party.

“A big stable lead for one political party is a very boring story,” said Robert Ford, a professor of political science at the University of Manchester, noting that the polls had barely budged for six months. “A lot of this reflects a much higher level of scrutiny and a desire for conflict and drama.”