Sen. Rob Portman is a Protestant, as is former Gov. Tim Pawlenty, who converted from Catholicism.

“I do not know of a presidential ticket in history that did not include at least one candidate affiliated with a Protestant denomination,” says Thomas S. Kidd, a Senior Fellow at Baylor University’s Institute for Studies of Religion. “That, in itself, would make Romney’s selection of a Catholic as his running mate historically significant.”

There was a time when this would have been a huge deal. John F. Kennedy, America’s first and (so far) only Catholic president, famously balanced his ticket by selecting Lyndon Johnson, a southerner and a Protestant.

But as Stokes notes, the likely possibility that Romney might select a Catholic “shows the great changes since 1960 (and 1928 before that) when a candidate’s Catholicism was seen as an impediment to electoral success.”