LONDON — This time he went too far. If a Western head of state had echoed Adolf Hitler, as Mahmoud Ahmadinejad did this week, would Europeans have shrugged their shoulders and dragged their feet over sanctions?

Yet it seems that the Iranian president is now licensed to blame “Zionists” for everything from the economic crisis to “the whole world order,” to threaten Israel’s existence and to use words like “cesspool” to describe its people. There was a deafening silence in Britain. Prime Minister Brown was too preoccupied with his own survival, making yet another “life-or-death speech” at his Labor party conference. The Conservative leader, David Cameron, also ignored the scandal.

For the press, too, this was old news, and not even the intended victims raised much of a protest. The Times of London, determined to impress its readers with the gravity of the story, ran the story accompanied by a fetching photograph of Carla Bruni.

Some have compared Mr. Ahmadinejad’s language to that of the Nuremberg rallies. That is not entirely accurate. It actually reminded me of Heinrich Himmler’s notorious speech at Posen in October 1943, in which he explained why the Nazis wanted to exterminate even Jewish children, to “make this people disappear off the face of the Earth,” so that future generations of Jews could never avenge their parents. Like Himmler, Mr. Ahmadinejad claims that his own people — and Muslims more generally — are threatened by “Zionists,” exploiting the paranoia of the Islamic world to justify turning Iran into a single gigantic nuclear suicide bomb.

But if there is little difference between Mr. Ahmadinejad’s murderous intentions and those of Hitler and Himmler, there is a considerable difference in the openness with which he talks about them. Himmler’s speech — one of several occasions when the S.S. leader was frank about the aim of annihilating the entire Jewish people — was given to an invited audience of party bosses, including Joseph Goebbels and Albert Speer.

Years later, Speer tried to claim — falsely — that he had not been present at this occasion, in order to persuade the world that he had known nothing about the Shoah. In other words, the Nazis were secretive about showing the world the full enormity of their crime.

Not so Mr. Ahmadinejad, who speaks in the full glare of publicity at the United Nations in New York. True, he claims to be a friend of those Jews who are not “Zionists” and even praised Moses as a great prophet. But this rank hypocrisy is so transparent that nobody even pretends to take it seriously.

As Shimon Peres dryly observed, if Jews are all to return to the lands of their origin, why not start with Moses, who came from Egypt? Mr. Ahmadinejad knows very well that the Israeli people is not going anywhere. If Israel is, as he threatens, to be wiped off the map, then his Iranian Revolutionary Guards — the S.S. of our day — and their terrorist auxiliaries, Hamas and Hezbollah, will have to kill 6 million Israelis. That is why Iran’s Führer wants the bomb and why he must be stopped from building one.

The downplaying of the scandalous nature of Iran’s open threat to destroy Israel is itself a scandal. Only in America and in Israel itself is the threat taken seriously. Even there, some people miss the point. Barack Obama said that he was sorry that Mr. Ahmadinejad “had a platform to air his hateful and anti-Semitic views.”

The best that can be said about this is that the senator has a lot to learn. It’s not the platform but the views that matter — and Mr. Obama has still not explicitly ruled out meeting the Iranian president, reversing his notorious offer to do so earlier this year. I shall be surprised if John McCain does not raise this issue with him in their first TV debate tomorrow. Mr. Obama had better have a good reply ready.

Still, the primary responsibility for preventing a second Holocaust lies with the nations who carried out or permitted the first one: the Europeans. But Europe’s leaders are heading in the wrong direction.

It doesn’t matter much whether President Sarkozy shakes hands with his Iranian counterpart, but it does matter that he is doing much more than shake hands with President Assad, the leader of Iran’s closest ally, Syria, and with President Medvedev, the leader of Russia, which is blocking sanctions on the U.N. Security Council. Syria, as it happens, is reported to be massing troops on the Lebanese border, while Russia has sent nuclear-armed warships to the Caribbean.

These rogue states are not only accomplices in Mr. Ahmadinejad’s criminal enterprise, but threats to peace in their own right. Mr. Sarkozy, who holds the rotating presidency of the European Union, is making a big mistake if he thinks that Syria or Russia will detach themselves from Iran merely because he asks them nicely.

The time has come for the democracies to unite against Iran and its allies. The Iranians need to understand that their president is now an outcast from humanity and a fugitive from justice — for to threaten genocide is a crime against humanity. Unless there is a change of leadership in Iran, an air strike against its nuclear facilities is imperative.

The only question is who will be involved and when it will take place. If the democracies, led by Europe and America, showed their solidarity with Israel by signalling that they recognize Israel’s right of self-defense, there would be little that Iran and its allies could do — and the allies would most likely desert.

This newspaper has supported solidarity with Israel from the start. The last thing the free world needs now is for such a voice to fall silent.

Mr. Johnson is editor of Standpoint.