...if Americans want to protect themselves from Islamist terrorism, monitoring the mosques that foment it must be a priority. Needless to say, this must be done legally. Romney isn't proposing to do away with safeguards like judicial oversight and warrants issued only for probable cause. ''I don't want to change the rules," he emphasized in an interview last week. ''You can wiretap only when you comply with the Constitution."

The evidence that some radical mosques have been perverted into terrorist hatcheries has been mounting for years. The notorious Finsbury Park mosque in London incubated jihadists for holy wars worldwide; among its alumni are Zacarias Moussaoui, the alleged 20th hijacker, and shoe bomber Richard Reid. Brooklyn's Al-Farooq Mosque is where Sheik Omar Abdul Rahman, a rabid Egyptian cleric, incited his followers to bomb the World Trade Center in 1993.

Just last week, Hamid Hayat of Lodi, Calif., was indicted on federal terrorism charges; he is one of five suspected jihadis arrested earlier this year. All five attended the same Lodi mosque, and allegedly took direction from its two imams, Shabbir Ahmed and Adil Khan -- both of whom have now been deported to Pakistan.

Romney's position is the only responsible one. We will never be safe from terrorism so long as enemies within our borders keep spreading the plague of Islamist violence. Homeland security depends in part on monitoring those enemies and knowing what they're saying. Even when they're saying it in a mosque.