"Our progress in degeneracy appears to me to be pretty rapid," Abraham Lincoln wrote in 1855. "As a nation, we began by declaring that 'all men are created equal.' We now practically read it, 'all men are created equal, except negroes.' When the Know-Nothings get control, it will read 'all men are created equal, except negroes, and foreigners, and Catholics.'"

The Know-Nothings were a political party based on a ferocious fear of immigrants that flourished in the 1850s. We thought of them while watching Donald Trump and Ben Carson ensnare themselves on a barbed wire fence of anti-Muslim statements.

America was built by immigrants. But throughout our history, this nation has also exhibited an ugly streak of nativist Know-Nothingism. In the 1850s, the haters focused on Catholics from Ireland and Germany. Today, they agitate against Muslims from the Arab world and Latinos from Mexico.

But the judgment of history is very clear. The Know-Nothings -- so aptly and memorably named -- are always wrong. Each wave of newcomers does change America, but they change it for the better, and Lincoln understood that.

If the Know-Nothings were to win, Lincoln wrote, and compromise America's commitment to equality, "I should prefer emigrating to some country where they make no pretence of loving liberty -- to Russia, for instance, where despotism can be taken pure, and without the base alloy of hypocracy."

Trump is a direct descendant of the Know-Nothing tradition, helping to fuel the "birther" movement by repeatedly questioning Barack Obama's national origins and religious faith. In 2011, he told Fox News that the president "doesn't have a birth certificate. He may have one, but there's something on that, maybe religion, maybe it says he is a Muslim."

Trump's Big Lie bombast has exploited our latent xenophobia. In a recent CNN/ORC poll, 29 percent of Americans said Obama is Muslim; that number jumps to 43 percent among Republicans, and 54 percent among Trump supporters.

So it was totally in character for an audience member at a town hall in New Hampshire to tell Trump, "We have a problem in this country; it's called Muslims. Our current president is one. We know he's not even an American ... When can we get rid of them?"

Not only did Trump decline to correct the questioner, he sympathized with him. "A lot of people are saying that," the candidate replied. "We're going to be looking at a lot of different things."

Later, Trump tweeted that he was not "morally obligated to defend the president," and that's true. But he IS morally obligated to tell the truth, to end the lies, to stop appealing to the worst angels of our nature instead of the better ones.

Carson was equally guilty when he said on "Meet the Press" that he "absolutely would not agree" with electing a Muslim president. His spokesman later explained Carson's reasoning: "There is a huge gulf between the faith and practice of the Muslim faith and our Constitution and American values."

Like Trump's accusations about Obama's roots, that statement is flat-out false. The Constitution could not be clearer: "No religious test shall ever be required as qualification to any office or public trust under the United States."

But religious and racial animosities are never far below the surface in American politics. In 1856, John C. Fremont, the first presidential candidate of the new Republican Party, had to prove he was not a Catholic before he could run. In 1960, John F. Kennedy, the only Catholic president so far, had to prove he was not beholden to his church or its leader before he could win.

In his famous speech to a group of Houston ministers, Kennedy warned, "This year it may be a Catholic against whom the finger of suspicion is pointed, in other years it has been, and may someday be again, a Jew -- or a Quaker or a Unitarian or a Baptist."

"Today I may be the victim," he concluded, "but tomorrow it may be you -- until the whole fabric of our harmonious society is ripped at a time of great peril."

Kennedy was not saying that religion has no place in public life. The presence of Pope Francis and the power of his words remind us how important religion can be as a touchstone of moral action.

But JFK's message remains prescient 55 years later. There should be no religious test for office. We should not fear those who worship different gods; we should embrace them.

And we should never let the haters prevail.