Donald Trump is now the Republican nominee for president. He still says he plans "a total and complete shutdown of Muslims entering the United States until our country's representatives can figure out what is going on," according to a December 2015 press release from the Trump campaign.
Lawmakers on both sides of the aisle, as well as world leaders, have called Trump's proposal unlawful and unconstitutional. But is it?
It's not the first time a U.S. president has moved to block specific migrant groups from entering the country, and there are loopholes in current federal law that could make Trump's ban possible.
In fact, the last six presidents have shut U.S. borders for certain groups of people. Most famously, Jimmy Carter banned Iranians during the Iran hostage crisis.
Carter did this using his executive authority under the 1952 Immigration and Nationality Act, which gives the president the power to deny entry to immigrants that are deemed "unlawful, immoral, diseased in any way, politically radical etc."
Ronald Reagan used the same power to block immigrants five times while he was in office, including a 1981 ban on "any undocumented aliens arriving at the borders of the United States from the high seas" and a 1986 ban for Cubans.
...denying immigrants who were unlawful, immoral, diseased in any way, politically radical etc.
Even President Obama has issued entry bans. In July 2011, he blocked "anyone under a UN travel ban; anyone who violates any of the 29 executive orders regarding transactions with terrorists, those who undermine the democratic process in specific countries, or transnational criminal organizations."
Could "President Trump" use the same power to ban Muslims? Maybe.
Ilya Somin, a law professor at George Mason University, told Circa that while Trump, under current law, could not enact a complete ban on Muslim entry, he could use his executive authority to direct the State Department to make it harder for Muslims to obtain visas.
"It's not entirely clear where the limits are, but there's a lot of room for abuse," Somin said.
Another way Trump could get his ban passed is to get Congress on his side. The Supreme Court in the late 19th century set a precedent by giving Congress virtually unlimited power over immigration law.
But would Congress pass legislation banning Muslims? It's highly unlikely, but then, that's what many people said about Trump becoming the Republican nominee.
They cast themselves as a party of religious freedom. I really would hate to see such hypocrisy to occur.
Robert McCaw, the Council on American-Islamic Relations (CAIR) government affairs manager, said that kind of law would be hypocritical coming from a Republican Congress.
"They cast themselves as a party of religious freedom. I really would hate to see such hypocrisy to occur," he said. "Should that hypocrisy occur, I don't think they might have enough votes to get it passed."
But Congress has also passed massive immigration bans before, including the Chinese Exclusion Act in the late 19th century, and again when the nation closed its borders to Jewish refugees fleeing the Nazis during World War II.
"The bottom line is that most if not all such laws and restrictions did enormous harm to both the potential migrants and to America as well and we should learn from that experience and be wary of repeating it," Somin said.
Muslims in the U.S. are already worried about what will happen in November.
"They're afraid that their grandmothers can't visit their children, they're afraid that they wont be able to see family members and that this would disrupt their own family lives," McCaw said.