Updated

For months, Republican presidential candidates have steadily escalated their rhetoric about the place of Muslims in the United States.

A Muslim shouldn't be president. Muslims fleeing war-torn Syria and Iraq should be barred from the U.S. Mosques should be under surveillance and shut down if people are radicalized in the places of worship.

Republican front-runner Donald Trump's call Monday for a "total and complete shutdown of Muslims entering the United States" was the latest salvo for a party aggressively testing the boundaries between concerns about security and discrimination against a religious group.

For most of Trump's rivals in the 2016 race and numerous other Republicans, it was also the proposal that finally crossed that line.