LONDON -- Ed Miliband, the leader of the opposition Labour Party, appeared to have Prime Minister David Cameron on the ropes. Mr. Cameron had just lost a vote in Parliament on a nonbinding motion to consider military action in Syria over chemical weapons, the first time in at least a century that a prime minister had not gotten parliamentary support for war. Mr. Cameron threw in the towel.
But Mr. Miliband, whose own position on the issue kept shifting, did not seize the moment, neither that night, Aug. 29, nor in the next days. He neither spoke convincingly to the nation about the nature of its alliances, its foreign policy or its values, nor did he attack Mr. Cameron effectively for mismanaging the entire issue. In a sense, both major party leaders showed themselves unable to master their own restive parties.
After three years as head of Labour, Mr. Miliband, just 43, has not managed to convince the British public that he is prime ministerial material. Questions about his leadership will hang over his party's annual conference, which begins Sunday.
In the words of a columnist for The Guardian newspaper, Michael White, Mr. Miliband, while having good instincts, "flickers rather than shines."
John Curtice, professor of politics at Strathclyde University in Glasgow, said more bluntly that polling shows that "Mr. Miliband is clearly not a help to his party and he may well be a hindrance." The coalition government of the Conservative Mr. Cameron and the Liberal Democrat Nick Clegg is unpopular, Mr. Curtice said, but there are deep doubts among voters about whether Mr. Miliband believes in anything very strongly.
"People are unclear what he stands for," Mr. Curtice said. "It's not just that he's seen as geeky or intellectual, he hasn't managed to show people that he has a vision and a sense of direction. There's a lack of definition."
Mr. Miliband, who became the Labour Party's leader three years ago -- after a devastating election defeat that ended 13 years of Labour government -- always had a huge task ahead of him, even with new elections not expected until May 2015.
"He became leader a few months after his party was rejected comprehensively," said Peter Kellner, a political analyst who runs a polling firm, YouGov. "He was a cabinet minister and close to Gordon Brown, so he was implicated in the wider reputation of a government that failed. Any new Labour leader would have trouble combating that."
Mr. Miliband, Mr. Kellner said, "has plainly not managed to break through as a person -- there are mountains of data on our Web site on how he is not regarded as strong or tough or up to the job as prime minister."
In any case, Mr. Kellner noted, Britons historically give new governments a second chance. It has been decades since a party new to opposition won a majority government after a single term.
Mr. Miliband has real strengths, beyond intelligence and decency. He did not support Britain's involvement in the Iraq war, which so badly damaged Tony Blair, and he boldly opposed Rupert Murdoch's powerful media empire in the wake of the phone-hacking scandal.
"In my view, Ed's leadership has been characterized by courage, resilience and a determination to stand up for families who have borne the brunt of economic tough times," said Stewart Wood, a close adviser to Mr. Miliband. "He stood up to Rupert Murdoch, he stood up to David Cameron on Syria, and he has not been afraid to say that Labour has to turn the page from the Blair/Brown years."
Mr. Wood said that Labour's emphasis on how to "reverse the decline in living standards that face most people in our country" will help the party regain popularity. With the economy finally improving and the election more than 18 months away, Labour will argue that a modest recovery will benefit only a small slice of British society that needs no help.
Part of Mr. Miliband's problem stems from his past as a bright young aide and then minister in Labour governments, and part comes from the residue of his extraordinary decision to run for the leadership against his older brother, David Miliband, who was a more senior figure, having been foreign secretary. It was an openly Freudian struggle, which the younger Miliband won narrowly with the help of trade union votes -- David Miliband had come out ahead among Labour lawmakers and party members.
Mr. Miliband had struggled to lose both the taint of fratricide and the stain of being beholden to trade union bosses, who are not the most popular figures in Britain. To avoid further speculation, David Miliband finally quit his own seat in Parliament and left the country, recently beginning a new job in New York as the head of the International Rescue Committee, a nongovernmental organization aiding refugees.
Mr. Cameron highlights the influence of union leaders whenever possible. So recent claims that a union had rigged the selection of Labour's candidate to fight a parliamentary seat in Falkirk, Scotland, proved highly embarrassing.
Mr. Miliband set up an inquiry, which found no rules were broken. But more boldly, in an effort to show decisiveness, he also announced plans to end the automatic affiliation to Labour of some three million union members unless they specifically ask otherwise. While union members will still be invited to join the party, Labour faces an inevitable and significant drop in financing.
Still, recent statements suggest that unions may retain significant influence over some Labour decision making, prompting claims that Mr. Miliband is backtracking and will accept a half-measure. His allies argue that an overhaul will be more successful step by step. But he may gain little credit anyway, Mr. Curtice said, given the perception that he was forced into change by the Falkirk controversy.
Were Mr. Miliband a Tory leader with similar ratings, Mr. Kellner said, he would be subject to a possible putsch. But Labour has little tradition of dumping its leaders.
Mr. Cameron and Mr. Clegg are not themselves especially popular. Mr. Clegg is considered to have sacrificed crucial elements of his electoral agenda to get his party into the governing coalition, and is clearly the junior player to Mr. Cameron.
Mr. Cameron has overseen tough years of economic austerity and recession, and he is being outflanked on the right by an anti-European party known as the United Kingdom Independence Party, or UKIP.
Mr. Curtice thinks that Labour should be significantly farther ahead in the polls than now; its lead over the Tories has shrunk considerably since early summer. Still, he said, given an electoral system that favors Labour because of the distribution of its voters, the unpopularity of the Liberal Democrats and slippage of Conservative votes to UKIP, "the Labour Party might win by default."
This article originally appeared in The New York Times.