Donald Trump's declaration Monday that the U.S. should bar any Muslims from entering the country was a sharp rejection of President Obama's speech a day earlier, when he pointedly urged Americans to avoid adopting anti-Muslim sentiments.
And the proposal escalates an intense debate already happening in American politics about religious tolerance, Islam and terrorism.
Trump's proposal, issued in a two-paragraph press release, was vague, unrealistic, potentially unconstitutional and very unlikely to be adopted as law.
It was almost universally condemned by people in both parties, including several of Trump's rivals in the GOP 2016 presidential campaign, with South Carolina Sen. Lindsey Graham calling it "downright dangerous."
But Trump's words may still have impact.
Congressional Republicans and the Obama administration are right now debating a bill to fund the federal government that the GOP is insisting include a measure that would limit the ability of refugees from Syria to enter the U.S. Polls show most Republican voters and even many Democrats are wary of accepting Syrian refugees.
Trump's position of stopping Muslims from entering the U.S. from any country, including Syria, pushes this political debate further to the right. It could harden the resolve of Republicans in Congress, who could demand that Obama sign the anti-refugee provision or risk a government shutdown.
More broadly, Trump's proposal illustrates the political divide in America about Muslims and Islam in the wake of the shooting last week in San Bernardino by a couple who U.S. officials say were radicalized and sympathetic to ISIS.
On Sunday night, in addressing the shooting in San Bernardino and his plan to fight ISIS, Obama repeatedly called on Americans not to link the broader Muslim community with ISIS.
"Muslim Americans are our friends and our neighbors, our co-workers, our sports heroes — and, yes, they are our men and women in uniform who are willing to die in defense of our country," he said.
He added, "It is our responsibility to reject religious tests on who we admit into this country. It's our responsibility to reject proposals that Muslim-Americans should somehow be treated differently."
The statement by Trump, currently leading in many polls of the Republican field, was a firm rejection of Obama's approach. Trump directly called for a religious test, one that would specifically target Muslims.
He did not attempt to separate radical Islamic terrorists from other Muslims. Trump cited polling data he says shows "there is great hatred towards Americans by large segments of the Muslim population," and called for keeping all Muslims out, in effect suggesting it was too hard to determine which Muslims were terrorists and which were not.
"Where this hatred comes from and why we will have to determine," Trump said in his statement.
Trump's campaign has been defined by his controversial remarks about ethnic and religious groups, from blacks to Mexicans to Muslims. But Trump is speaking for a broader constituency, with polls showing that many Republican voters back the mogul in part because of his opposition to illegal immigration and Syrian refugees.
And his discomfort and concerns about some Muslims is not unique. Some of the more moderate Republican candidates, such as ex-Florida Gov. Jeb Bush, have said only Christian refugees from Syria should be admitted into the U.S., in effect illustrating wariness about Muslims from abroad and calling for the kind of religious test Obama opposes.
A recent survey conducted by the non-partisan Public Religion Research Institute found deep reservations from Americans about Islam, particularly from conservative-leaning parts of the electorate. According to the survey, 56 percent of Americans overall agreed with the statement that, "The values of Islam are at odds with American values and way of life."
The majority of self-described Democrats disagreed with the statement, but 76 percent of Republicans agreed with it, as did 73 percent of white evangelical Christians and 77 percent of people who consider themselves part of the Tea Party movement.
And these surveys were conducted before the attacks in Paris and San Bernardino.
If Trump were to win the GOP nomination, he would have a national platform to press forward his controversial views on Muslims, with the Republican Party in effect having endorsed his candidacy.
But even if Trump is not the GOP nominee, the country appears to be undergoing a shift in how it views Muslims in the wake of the rise of ISIS.
"I also want to speak tonight directly to Muslims throughout the world. We respect your faith. It's practiced freely by many millions of Americans and by millions more in countries that America counts as friends. Its teachings are good and peaceful, and those who commit evil in the name of Allah blaspheme the name of Allah," President George W. Bush said in an address to Congress on Sept 20, 2001, less than two weeks after the World Trade Center attacks.
He added, "The terrorists are traitors to their own faith, trying, in effect, to hijack Islam itself. The enemy of America is not our many Muslim friends. It is not our many Arab friends."
It is very unlikely one of the Republican candidates today would describe Islam in such terms.