Omid Safi

Shortly after teenagers beat up a Columbia University physician Saturday, a Muslim woman was attacked a few blocks away.

It is not clear whether the attacks on Dr. Prabhjot Singh and the Muslim woman, who were both treated at Mount Sinai Hospital in New York, are related. But many say the motives, if not the perpetrators, are depressingly familiar.

They are part of a long line of assaults on Sikhs, who are sometimes mistaken for Muslims; on Muslims; and, more generally, on people perceived as foreigners.