Over the course of his campaign, Donald Trump has repeatedly made bold, and sometimes surprisingly divisive, policy proposals. It's part of his pitch to voters: "We can't worry about being politically correct." And during the Republican primary season, when there is a premium on appealing to conservative voters, it was a tactic that clearly set him apart from his rivals.

But Trump has also walked back several of his most divisive proposals. "Of course" the border wall is negotiable, he told Sean Hannity in February. Likewise, his proposed ban on Muslims entering the United States became, over time, "negotiable."

It didn't start out that way. When Trump first announced the proposed ban at a rally in South Carolina in December, to raucous applause and a standing ovation, he called for a "total and complete shutdown" of Muslims entering the U.S.

But his tone soon shifted. Just a few days later, he promised the ban would be "temporary." By March, he allowed for "exceptions" to the ban, though he was criticized for telling MSNBC moderator Chris Matthews that he'd specifically make exceptions for some of his wealthy Muslim friends. And by May, everything was "up for negotiation."

"I can't make these decisions myself," he said in a May 5 interview with Fox News's Brett Baier. "We have Congress ... we have to deal with a lot of people. I can't just take executive orders like Obama."

A few days later, on "Fox and Friends" host Brian Kilmeade's radio show, Trump said the ban was "just a suggestion" that "hasn't been called for yet."

But when Trump delivered a foreign policy speech Monday, he seemed to double down on the ban.

"When I'm elected, I will suspend immigration from areas of the world where there is a proven history of terrorism against the United States, Europe or our allies, until we fully understand how to end these threats," he said.

Immigration is a bit more specific than a "total and complete shutdown" of Muslims entering the country (tourist and business visas aren't the same as work permits, permanent residency status or "green cards," for example). But it seems Trump is sticking by his general idea – even if we can't be sure what exactly he means by it.