France’s interior ministry reported last year how Islamic supremacists, specifically the Muslim Brotherhood, use “entryism” to infiltrate and subvert the country’s democratic institutions. This spring, the French Senate adopted legislation seeking stronger authority to detect and prevent entryism, which confiscates the vocabulary of civil rights and leverages Western protections of minority equality to make societies more Islamic.It may be too late for France, given two generations of large-scale, often unassimilated immigration from Muslim-majority countries, expansion of urban neighborhoods virtually off-limits to authorities, and influence within them of both anti-Western imams and criminal gangs. The United States is not Europe, but...