Jeremy Corbyn at the British Labour Party’s annual conference. PHOTOGRAPH BY BEN PRUCHNIE / GETTY

On Tuesday afternoon, Jeremy Corbyn, the new leader of the British Labour Party, delivered a long speech at the party’s annual conference. His remarks left his audience cheering, and even garnered grudging praise from some of his critics. Having been portrayed in some quarters as a fire-breathing Marxist and a danger to the security of the United Kingdom, the sixty-six-year-old leftist sounded more like the Archbishop of Canterbury, defending the values of fairness, social justice, and solidarity with the downtrodden, and calling for “a kinder politics, a more caring society.”

While the Sun, Rupert Murdoch’s mass-market tabloid, dismissed Corbyn’s speech as “incoherent, dishonest, irrelevant, pitiful drivel,” the Daily Mail, another right-wing newspaper, acknowledged, “Those who hoped to see Jeremy Corbyn fall flat on his face—and there were plenty, both inside and outside his party—were in for a disappointment.” Quentin Letts, one of the Mail ’s political columnists, described Corbyn as a “bearded codger” in an “Oxfam-issue jacket,” but also said, “It is hard to feel personally threatened by him, dotty and dangerous though his ideas might be.”

Coming from the Mail, a paper whose animosity toward the Labour Party goes back at least to 1924, when it published, just prior to an election, the notorious Zinoviev letter, that was high praise. In the febrile echo chamber that is Westminster/Fleet Street, there was general agreement that it was Corbyn’s best moment since becoming leader. After watching his speech, Steve Bell, the Guardian’s famous editorial cartoonist, portrayed him as a sly, bushy-tailed fox. “I think he’s going to start worrying the Tories quite soon,” Bell said in a short video posted on the Guardian Web site, “because he’ll be saying things directly, simply—saying things in an uninhibited way—which the Labour Party has not been doing for years.”

On Wednesday, Corbyn should have been enjoying the moment. But, rather than doing that, he created a gaping rift with some of his own colleagues by telling an interviewer from the BBC that, if elected Prime Minister, he wouldn’t use Britain’s nuclear weapons to defend the country. While Corbyn had previously made clear his opposition to nuclear weapons and his wish that Britain refrain from replacing its aging Trident missiles with a costly set of new nukes, this was something more: an emphatic statement that, regardless of the circumstances, or of official Labour Party policy, which currently supports the U.K.’s nuclear deterrent, Corbyn personally would never order Britain’s military to press the button. Given several chances to withdraw or amend his answer, he declined to take them.

It didn’t take long for a backlash against Corbyn’s remarks to spread. Within hours, Maria Eagle, the shadow defense secretary, whom he appointed just a couple of weeks ago, publicly criticized him. “It undermines, to some degree, our attempt to try and get a policy process going,” Eagle told the BBC. “As far as I am concerned, we start from the policy we have. I don’t think that a potential Prime Minister answering a question like that in the way he did is helpful.” Other members of the new shadow cabinet also chimed in, with several appearing to question their boss’s understanding of basic military logic. “If you’ve got a nuclear deterrent, you have got to be willing to use it in extreme circumstances, or it isn’t a deterrent,” Lord Falconer, the shadow justice secretary, said. One trade-union boss who supports Labour, Paul Kenny, the general-secretary of the G.M.B., even suggested that Corbyn would have to accept the party’s official policy or resign.

If, for Labour, this were the sort of healthy internal debate that Corbyn had promised to encourage, it was also a gift to the party’s opponents, and it prompted Prime Minister David Cameron to reiterate his charge that Labour under Corbyn couldn’t be trusted with Britain’s national security. As I read the Prime Minister’s statement, which he made from Jamaica, doubtless with great glee, I was reminded of Steve Bell’s cartoon—and also of Isaiah Berlin’s famous essay “The Hedgehog and the Fox,” in which he distinguished between thinkers who look at the world on the basis of a single defining idea (the hedgehogs)and those who draw on different ideas depending on the situation (the foxes). While Corbyn’s conference speech, which included some clever putdowns of his press critics, suggested to Bell and others that there was something vulpine about him, the Labour leader’s response to the BBC interviewer suggested that he was a spiky-backed creature with a tendency to roll into a ball and refuse to move.

For a left-wing protest politician, which Corbyn has been for more than thirty years, it is fine, and perhaps even imperative, to have a single, all-encompassing world view. Corbyn believes that the domestic and international status quo is fundamentally unjust, and that so are most, if not all, of the pillars on which it rests, including the division of the world into nine nuclear powers (the P5 countries, plus India, Israel, Pakistan, and North Korea) and everybody else.* “We are not in the era of the Cold War anymore; it finished a long time ago,” he told the BBC. “I am opposed to the use of nuclear weapons. I am opposed to the holding of nuclear weapons. I want to see a nuclear-free world. I believe it is possible.”

This was more of the plainspokenness that Bell had identified in Corbyn, and in many ways it is admirable. Rather than deflecting the question, as most politicians would have done, Corbyn gave the honest answer that his conscience dictated. But it does raise the issue of whether he can combine his moral fervor with the flexibility, and the nous, that any democratic leader needs.

Before his statement on Wednesday, Corbyn had said that he would abide by the Labour Party’s official policy toward nuclear weapons, while also endeavoring to change it in an open internal debate. That was the foxy thing to say. In addition to being politically astute, it recognized the philosophical point that there can be clashing goods—in this case, the duty to follow one’s conscience, the obligation of a party’s leader to respect its policies, and the need to win over the public before making sweeping policy changes. If Corbyn wants to prove his critics wrong and enjoy a successful term as Labour’s leader, he would be well-advised to go back to that stance, shaking his bushy tail along the way.

*This post was updated to correct the number of nuclear powers.