This article reconsiders the legacy of American Puritanism in the context of the current controversy around “radical Islam.” The rise of Salafi jihadism has emboldened those who maintain that Islam is incompatible with Western secularity. Liberal responses to this claim frequently appeal to the United States’ allegedly Puritan past, suggesting that the United States is particularly well placed to deal with both radical Islamism and anti-Islamic prejudice because of the ecumenical pluralism that emerged from the colonial crucible of competing denominations. I interrogate this claim by reading liberal and conservative statements about Muslims in the contemporary United States alongside the writings of Roger Williams, whom many consider to be the father of American pluralism. I argue that the modern rhetoric of religious diversity mirrors the eschatological structure of Williams’s tenet of toleration, wherein Muslims are offered only temporary acceptance. In each case, the pluralism of the present is set off against an anticipated cultural homogeneity.