On September 11, 2001, a struggle took place over the skies of Pennsylvania as passengers on United Flight 93 tried to regain control of the aircraft from the terrorists. It was the first instance of homeland resistance to jihad.

Fifteen years later, the jihad threat is bigger than ever. Now as then, it must be resisted, but for the most part it will be a different kind of jihad that we will face, and it will call for a different kind of resistance.

The passengers on Flight 93 are remembered as heroes. But if you try to resist the most common form of jihad, you probably won’t be hailed as a hero. It’s more likely that you’ll be smeared as a racist or an Islamophobe. You might even be hauled into court.

Most Americans think of the Islamic threat mainly in terms of armed jihad, but there is another form of jihad that we have to contend with, and armies are powerless against it. It’s called stealth jihad or cultural jihad, and it can be just as effective as the armed variety. Stealth jihad is a long-term campaign to spread Islamic law and culture by influencing key institutions such as churches, schools, courts, businesses, media, and local and national government.

Armed jihad instills a sense of urgency—“let’s roll,” let’s take action. But stealth jihad is intended to lull us into complacency—not “let’s roll,” but “let’s roll over and go back to sleep.” Immediately after ⁹⁄₁₁, representatives of various stealth organizations such as CAIR and ISNA were at President Bush’s side, assuring him that Islam means “peace.” Bush, in turn, assured the rest of us that the terrorists were a tiny minority who had attempted to hijack a great religion. Amazingly, fifteen years later, that myth is still the dominant narrative.

The term “stealth jihad” is a bit misleading. The stealth jihad groups may be stealthy, but they don’t operate underground. They have offices, spokesmen, PR people, legal teams, and impressive websites. They present themselves as moderate mainstream groups, and for the most part the media and administration officials accept them as such.

How do they operate? In general, they advertise themselves as civil rights advocates working to protect the rights of the “Muslim community.” Using the cover of civil rights activism, the stealth jihadists have been able to score some spectacular successes. In 2012, for example, more than 1,000 documents and presentations were purged from counterterror training programs for the FBI and other security agencies. This was done in response to pressure from Islamic advocacy groups who complained that the training policies were biased and offensive to Muslims. In effect, these Muslim Brotherhood-linked groups were given veto power over national security policy, and, as a result, investigative agencies were forced to limit themselves to politically correct policing.

America’s commitment to the dogma of political correctness is, in fact, the chief factor that accounts for the success of stealth jihad. The stealth jihadists are well-versed in the rules of political correctness, and they know how to use them to their own advantage. And if they can bend the federal government to their will by using these methods, they can certainly do the same to average citizens.

Suppose, for instance, that you are a teacher and a Muslim boy brings a suspicious device into your classroom that looks like it could be a bomb. Do you call the police or do you look the other way? That was the situation that faced teachers at an Irving, Texas school two years ago. In this case, the police were called and Ahmed Mohamed, aka the “clock boy,” was detained and questioned. Almost immediately, the social elites rushed to the defense of young Ahmed. He was hailed by the PC media as a civil rights hero, and the police and school teachers were smeared as redneck racists. Subsequently, the boy’s family sued the town of Irving for 15 million dollars.

Had they intended to do that all along? It’s difficult to say, but it fits the pattern of stealth jihad operations: create a provocation and then when the target responds in the expected way, sue them in the confidence that they will settle to avoid bad publicity. The aim of such “lawfare” operations is not so much to collect big sums as to create a chilling effect that inhibits criticism of or investigation into Muslim activities.

Let’s take another example. Suppose you are a store manager or a small business owner. Suppose an employee demands to wear a hijab at work. Or suppose a group of employees demands prayer breaks during the day. What will you do? Do you want to face a lawsuit? Is a prayer break the hill you are prepared to die on?

That’s the way stealth jihad works. It’s difficult to resist because all our conditioning in political correctness urges us to equate resistance with bigotry and intolerance.

Here’s one more example. Suppose you are in charge of hiring baggage handlers at an airport or suppose you do the hiring for some concession or vending firm that operates within the airport. Suppose you have suspicions about a Muslim applicant for a job. Do you subject him to extra scrutiny? Do you ask him questions that you would not ask other potential employees? Do you want to be transferred or even fired? Do you want to be the target of a lawsuit with CAIR’s lawyers representing the applicant you “humiliated”?

These seem to be the questions on the minds of the people who actually do the hiring. Judging by the number of terrorists and would-be-terrorists who were able to secure airport jobs—often with security clearance and access to planes—political correctness affects the vetting process even in those places where vigilance is most needed.

The two jihadists who bombed the Brussels airport worked at the Brussels airport. Terry Lee Loewen, a Muslim convert who planned an attack on Wichita’s Mid-Continent Airport, worked in the airport as an avionics technician. Two suicide bombers for al-Shabaab worked at the Minneapolis airport, and a third Minneapolis airport worker was killed while fighting for ISIS in Syria. In 2015, a Department of Homeland Security report revealed that at least 73 people hired at US airports had suspected links to terrorists or terrorist activity.

Political correctness provides stealth jihad with immunity from close inquiry. Consequently, stealth operations can be more difficult to detect and resist than the armed variety. On United Flight 93 there came a decisive moment when everyone understood what was happening, and what had to be done. That was when the battle cry was “Let’s roll!” But the war with stealth jihad doesn’t provide us with such clarity. It doesn’t provide us with definitive “let’s roll” moments.

We’re in a different kind of struggle than the passengers on Flight 93. Our situation is far less terrifying than theirs, but also considerably less clear. Stealth jihad doesn’t concentrate the mind; rather, it has the effect of confusing it—of keeping us off-balance by appeals to tolerance and non-discrimination. Nevertheless, at some point soon we will have to roll back the stealth jihad campaign before it rolls over us.