The British Muslim “hate preacher” Anjem Choudary has finally been convicted after 20 years of preaching fundamentalist Islam aimed at radicalizing young Muslims and encouraging them to engage in terrorist activities. Last week, he, along with Mohammed Rahman, was found guilty of inviting support for ISIS in speeches and lessons posted online. Choudary’s case, and his long history of Salafist extremism, exemplifies the difficulties that we in the West face in dealing with homegrown Islamic radicalism.

Choudary, a British citizen born to Pakistani parents, has spent two decades working toward global Islamic domination. These are his words. He wants Islamic law to spread throughout the world, and told the Washington Post in 2014 “We believe there will be complete domination of the world by Islam.” He has also said that “Britain belongs to Allah.”

Choudary founded multiple Islamist and Wahhabist organizations in England, all of which were eventually banned. He has connections with numerous other Salafist and Islamist groups and is a known leader of “dark networks” that stretch across Europe and seek to radicalize young Muslims. He has praised terrorists, including the 9/11 attackers, and proclaimed they are in paradise. He has been friendly with a top ISIS figure and executioner, who at the time was part of the terrorist group Sharia4Belgium, and is connected to more than 100 British terrorists, and many terror plots.

Terrorism’s Victims Include Freedom of Speech

But somehow Choudary has managed to skirt the law all these years. A lawyer until 2002, he knew how to step up to the line of criminality without crossing it. Although his influence on European Muslims is well-known and -documented, he managed to skate by on technicalities of the law, because he hadn’t engaged in terrorist activities himself, nor was it proven he had directly sent people to Iraq and Syria to join ISIS.

What finally allowed authorities to arrest him last year and convict him this month was an oath he signed to ISIS’ leader, Abu Bakr al-Baghdadi, in conjunction with speeches posted online that called on Muslims to join ISIS. As a prohibited organization, membership in ISIS is considered a criminal offence. British authorities convicted him of “inviting support for a proscribed organization,” under Terrorism Act 2000.

Choudary’s case raises questions of how far freedom of speech extends, and what ought to be done with terrorists once convicted. Although freedom of speech in Britain is a long-established common law right, in recent years it has suffered many setbacks. A Reason magazine article from last year highlighted the policing and punishment of Twitter users and journalists, as well as advertisers (a notable case was an ad banned in London for supposedly body-shaming women by depicting a fit woman in a bikini).

But what about here in the United States? People often ask what we should be doing at home to protect our country from Islamist terrorism. While presidential candidate Donald Trump would point solely to immigration, this misses the glaring fact that many Islamist terrorists were born in America or came as young children. This list includes Omar Mateen (Orlando), Faisal Mohammed (University of California-Merced), the Tsarnaev brothers (Boston Marathon), Syed Farook (San Bernardino), Nadir Soofi (Garland, Texas), and Nidal Hassan (Fort Hood).

Terrorists like these are drawn to Salafist Islam either in their communities and mosques or on the Internet. It isn’t always clear what the authorities can legally do beyond monitoring radical clerics and mosques and looking for connections between radicalized individuals and groups. How far can they go in policing what Islamists are preaching?

It Would Be Difficult to Prosecute Choudary in America

Freedom of speech is perhaps the most crucial right in a free society. There’s a reason it was the first right enshrined in the Bill of Rights: it’s meant to protect citizens from government attempts to silence dissent and regulate ideas and messages. In America, a country with arguably the most robust free speech protections, there are only a few exceptions to this First Amendment right. These include speech others own, child pornography, commercial speech, obscenity, and fighting words. None of these, however, are applicable to combatting Islamists, who are essentially supporting terrorism without providing terrorists with direct material support like guns, bombs, or money.

The one type of unprotected speech that would be applicable in a case like Choudary’s is incitement to violence. Speech that advocates force is unprotected, but only if its intention is to produce “imminent lawless action” and is likely to succeed. This could potentially apply to the sermons of Salafist imams, which, if encouraging people to fight with ISIS, are promoting lawless action. However, proving that they’re likely to lead to imminent action is more difficult.

Expressing even the most reprehensible views is protected by the First Amendment, including having a Ku Klux Klan parade or arguing for the overthrow of the government. So an Islamist imam could preach beliefs whose natural conclusion might be violence, but so long as he isn’t calling on a crowd to go out right away and commit terrorism, his speech is protected. This is why we may not have been able to prosecute a man like Choudary here in America.

Another way unprotected free speech comes into play is “true threats.” This recently made news when a Missouri woman was arrested for retweeting Twitter posts calling for the murder of U.S. law enforcement officials. The tweet contained names, addresses and phone numbers. Federal prosecutors argue that her retweets are tantamount to active support of ISIS, and charged the woman with conspiracy and transmitting a threat across state lines. Her defense, based on First Amendment grounds, argues the charges are unconstitutionally vague, once again illustrating the tension between free speech and national security.

Prisons Aren’t a Great Place for Islamists, Either

Once a conviction is made, as with Choudary, the problems don’t end there. Choudary faces up to ten years in prison. But what will he do once behind bars? Prison systems have become notorious in Europe and America for breeding radical Muslims, so a man like Choudary poses a threat inside as well as outside of prison.

Islamists in prison are treated like “aristocracy,” according to an audit of French prisons. When Salah Abdeslam, one of the Paris attackers, was arrested and sent to the Fleury-Mérogis prison he was “welcomed as the messiah,” according to one guard there. That same audit also found jihadi inmates can easily communicate with the outside world, including Syria.

So officials face a difficult decision between keeping Islamists like Choudary in the general population, where they can influence and indoctrinate other men, or concentrating Choudary and others like him in cell blocks so they don’t have access to non-radicalized inmates. This, of course, has its own dangers, namely that these men may plan future attacks and terrorist operations together. The third option, total isolation, is widely unpopular in places like Britain and France, where it is, perhaps correctly, seen as inhumane and cruel.

Choudary’s stay in prison will last a maximum of ten years. Then what? Does he get out in a few years after having been active in prison, and go on as he did before? Perhaps this time he’ll be more careful so as not to get caught. Some countries are working on de-radicalization programs, but their success has been dubious.

Choudary’s case typifies the difficulties the Western world faces in combatting radicalization. As a country that is fundamentally based on concepts of liberty and freedom of speech and of association, our principles and constitutionally protected rights sometimes run up against threats to national security. This is the great challenge we will face in the fight against Islamist ideology and homegrown radicalization in the years ahead. For a sense of the challenges to come, we need only look to Europe, where that fight is well underway.