LONDON — Are the streets of Vienna echoing to the sound of jackboots again? Two anti-immigrant parties, the Freedom Party and the Alliance for the Future of Austria, achieved the far Right’s best result since 1945 in last weekend’s elections. They took 29% of the vote, dwarfing the 18% that the Nazis achieved when they made their breakthrough in Germany in 1930. These are parties that, while avoiding openly neo-Nazi policies, do support symbolic policies such as the legalization of public displays of the swastika. What does their triumph signify? Are we witnessing a re-run of the 1930s, when a Wall Street crash sent shock waves across Europe that swept Hitler to power?

As a journalist who observed the rise of Austria’s most notorious demagogue, Jörg Haider, during the Waldheim affair in the late 1980s, I have no doubt that the answer to this question is a resounding no. There is no enthusiasm for Hitler in Austria or anywhere else, except possibly in President Ahmadinejad’s Iran. The reason for the rise of such parties in Austria and many other European countries may be summed up in two words: immigration and Islam.

The problem is that the unprecedented mass immigration which Europe has experienced in recent years has coincided with a global jihad that takes both “hard” (terrorist) and “soft” (cultural) forms. In countries where a large percentage of the immigrants are also Muslims, the sense of a way of life under threat is particularly acute. Austria was for centuries a battleground in the confrontation between Christianity and Islam, and a slogan used by Heinz-Christian Strache, the Freedom Party’s leader — “Vienna must not become Istanbul” — indicates that the sense of a nation under siege still resonates.

It is true that the rhetoric used by Mr. Strache — warning, for example, against Muslim immigrants “fondling our Austrian girls” — is distasteful and reminiscent of Nazi anti-Semitic propaganda. Neither Mr. Strache nor Mr. Haider has any inhibition about exploiting sometimes irrational fears. But when the mainstream parties claim that what they call “Islamophobia” is mere paranoia, or that the rise of far-Right parties is based on nothing more than “populism,” they are deluding themselves.

For the ordinary voters of Europe have good reason to be worried about the rise of Islam. They are angry that the socialist, liberal, or conservative parties that run their democracies appear to have conspired to suppress all public discussion of their private anxiety about the future of their countries. And they are punishing these parties at the ballot box.

Until the centrist parties of Europe take on board the concerns of their electorates about both forms of jihad, the extreme Right will continue to gain. Nor is it sufficient to tighten immigration controls, as most governments are belatedly doing. The concentration of Muslims in the cities of Europe has already reached critical mass and has triggered a political shift towards appeasement by the authorities.

Take two recent examples from Germany and Britain. A fortnight ago, Cologne was convulsed by riots over the building of a huge new mosque to rival the city’s celebrated cathedral. The violence was caused, not by the protestors against the mosque, but by a much greater number of “anti-fascists” who successfully prevented them from demonstrating. The police stood by while the protest was crushed and the mayor hailed this shameful affair as a victory for democracy. It was, of course, nothing of the kind; rather, it was a victory for Islam.

Meanwhile in London last Friday Muslims firebombed the house of the Dutch publisher of “The Jewel of Medina,” a novel by an American writer, Sherry Jones, about the Prophet Mohammed and his child bride, Aisha. Although the police had received warnings and the fire was doused without any injuries, the publisher has gone into hiding.

On both sides of the Atlantic, self-censorship now silences debate about sensitive aspects of Islam more effectively than any traditional censor could have done. Twenty years after the Salman Rushdie affair, the Islamists have succeeded in their aim of intimidating the guardians of free speech and the free press.

So what is to be done? For a start, we must not allow the devil to have all the best tunes. By leaving it to the neo-, crypto-, and pseudo-fascists to raise the issue of how Islam is to be integrated into European society, the liberal elites have made a big mistake. Telling voters that it is fascist to object to the insidious Islamicization of their environs is liable to drive them into the arms of real fascists.

This is not to exonerate men like Mr. Haider. But he has learned over the years to curb his earlier tendency to make excuses for the Nazis, which doubtless had much to do with the fact that his wealthy family benefited from the expropriation of the Austrian Jews.

Nowadays Mr. Haider focuses on the future not the past — hence the name of his new party, the Alliance for the Future of Austria. The question he poses is the one the voters are asking themselves: does Austria, faced with demographic decline and multicultural insecurity, really have much of a future?

Under the circumstances a nation which has never felt at ease with its own identity will be tempted to vote for the leader who offers the most affirmative answer. There is no reason why liberal, socialist, or conservative leaders, too, should not defend Western values and explain to Muslims why they too are expected to adopt them. It is idiotic to leave that task to those whose own commitment to these values is dubious.

If Europe cannot face the challenge of Islam without electing demagogues, then our democracy is in much worse shape than we thought.

Mr. Johnson is the editor of Standpoint.