GEERT WILDERS should be feeling good. This week the Dutch MP launched a new political party—demanding a halt to non-western immigration to the Netherlands for five years and a tougher line against Islamic radicalism. Some national opinion polls already put his party in second place. But Mr Wilders admits he is not sleeping well. His life has been threatened by the Islamic radicals he excoriates and it is no longer safe for him to live at home. Instead he moves between safe houses, and can travel only in an armoured car, surrounded by bodyguards. “It's like being trapped in a B-movie,” he says.

The Dutch security services are taking no chances because three weeks ago Theo Van Gogh, a prominent Dutch film-maker who had made a movie attacking Islam's attitude to women, was murdered on the streets of Amsterdam. And this was not any old street killing. Mr Van Gogh was dragged from his bike, shot six times and his head was nearly sliced off by an Islamic radical, who then impaled a five-page letter attacking the enemies of Islam on the chest of his dying victim. Ayaan Hirsi Ali, a Dutch politician of Somali Muslim origin who was repeatedly threatened in the letter, is also in hiding and, unlike Mr Wilders, has not re-appeared in parliament. Other prominent politicians and even some journalists now have permanent armed protection. “You're nobody as a columnist unless you have an armed guard,” jokes one eminent Amsterdamer.

The current atmosphere in the Netherlands will provoke some knowing nods on the other side of the Atlantic. For some months, leading American intellectuals have been pointing to what they see as the growing threat to western Europe from militant Islam. At a recent seminar at the Brookings Institution, Francis Fukuyama argued that “Europeans are threatened internally by radical Islam in a much more severe way than Americans are in terms of their external threat.” According to Mr Fukuyama, Europeans have hitherto been deterred from debating the threat by a “stifling political correctness”. But events like the Van Gogh murder are changing the debate. It is increasingly common for mainstream European politicians to call for much tougher measures against Islamic radicals and a more aggressive insistence on western liberal values. These demands have been heard with increasing force in all the west European states with significant Muslim populations—including France, Germany, Britain and Belgium—but above all in the Netherlands.

There is broad agreement that some limits to inflammatory speech must be defined—but where to set those limits and what to do with those who overstep them is still deeply controversial. Some Dutch politicians are arguing that Muslim sensitivities should be catered for by strengthening the blasphemy laws—Mr Van Gogh had outraged Muslims by broadcasting pictures of verses of the Koran scrawled on a naked female body and referring to Muslims as “goat-fuckers”. But others respond that a strengthened blasphemy law would go in the wrong direction. “There is no way you can appease Muslim radicalism,” says one academic, “If you go down that route, you will end up banning the sale of alcohol in supermarkets.”

The debate on how to respond to Islamic radicalism has been made no easier by the confusion of several different arguments: about terrorism, about levels of immigration into Europe from the Islamic world and about the assimilation of immigrants. Some take an alarmist view of current demographic trends. Bernard Lewis, a British historian at Princeton University in America, said recently that by the end of the century “at the very latest”, the European continent would be “part of the Arabic west, the Maghreb”. This comment has been widely quoted—including by Mr Wilders in the Dutch parliament. But a glance at the figures suggests that Mr Lewis is a better Arabist than mathematician. At present there are not more than 13m Muslims in the European Union, out of a total population of 457m. Even if there is a massive surge of immigration and the fertility of white Europeans falls even further, it is difficult to see how this will lead to a merger between Europe and North Africa.

The demographic picture in particular places is admittedly more dramatic. The Muslim population of France is now nearly 10% of the total. And it is officially projected that the three largest Dutch cities will have 50% non-western populations (most of them Muslim) by 2020. Yet even these figures need not be alarming, if Muslim populations assimilate easily. It is here that traditional liberal attitudes are undergoing a re-think. For Mohammed B, the murderer of Theo Van Gogh, was not a marginalised or oppressed figure. He spoke excellent Dutch and was studying for a diploma. It looks increasingly apparent that—as with the 9/11 hijackers—the problem is not lack of integration or opportunity, but a vicious ideology.

Depending on the numbers of people gripped by this ideology, that conclusion could be re-assuring or worrying. The Dutch secret service reckons there are only about 150 Islamic radicals on the fringes of terrorism in the country. This suggests the problem could ultimately be treated as a law-enforcement issue, as with the Baader-Meinhof gang that terrorised Germany in the 1970s. But Mr Wilders quotes Dutch academics who estimate that around 10-15% of the Dutch population of 1m Muslims sympathise with jihadist ideology. He says that the 150 suspected terrorists should be deported or imprisoned immediately. But he also demands a similar fate for those Dutch citizens who endorse jihadist ideology, whether in print, in a sermon or in an internet chat-room. Mainstream Dutch politicians still recoil from such measures, believing them to be incompatible with traditional freedoms—and likely to radicalise Dutch Muslims further. Launching a war on terrorism is one thing; a civil war on terrorism is altogether more daunting.