Though we are a nation of immigrants, a segment of the American people has always wanted to walk through the door and then close it behind them, keeping everyone else out. This segment dates back most clearly to the nativist movement that took place in the years leading up to the Civil War. When the nativists have their way, the US stops being a nation united by principles of freedom and justice. We are unfortunately witnessing a resurgence of these politics. An understanding of their history, and the history of their defeat, could help to embolden the contemporary generation.
Only a few decades after the American Revolution, the "bad' folk were the Irish escaping from the famine and British oppression. Many of the nativists of that time were Protestant, mostly Presbyterian and Lutheran, living in Ohio, Massachusetts and Pennsylvania. One of the strangest parts of their story was their flag, which carried the banner "Native Americans Beware of Foreign Influence." Of course, none of the nativists were American Indians. In fact, Indians were branded as "bad' folks as well. 
The pre-Civil War nativists developed their own political party, the Know Nothings. They were influential for an entire generation. For them, the enemy was Rome and its adherents, especially the Irish and Italians. Later, the Irish Catholics in the West turned on the incoming Chinese, Japanese and black American labor. This ailment of anti-immigration is like flu in the midst of Christians. It comes and goes.
Right now, Trump, a Presbyterian, is returning to this tradition. His wall with Mexico, as with the Soviet wall for Eastern Europe and the Chinese wall, will not work. But Trump shows excitement at the reaction of Republicans who believe once again a wall can stop the "bad" folks from getting into our sacred country where only the true Americans live.
Consequences follow this madness, as pointed out in a brilliant Washington Post column by Catherine Rampell on August 27 of this year. Rampbell wrote "At what point, in this great nation of immigrants, did calling someone an "immigrant" become such an insult?"
Trump's campaigning with the forked tongue says he loves 'Mexicans" and "hires thousands of them" leaves behind the truth of the matter that these folks are part of the USA and will be if we are lucky. The infusion of people from around the world has brought in a work force, a medical doctor in every hospital in America and new companies with imagination and power. The real truth is we need immigrants.
We must keep in mind that that the ideas of people like Trump have led to considerable suffering throughout American history. Catholic churches were burnt down, and it only stopped when the Archbishop of Ireland went to the authorities and told them in short, if this continues, New York City will look like Moscow. Two hundred thousand Irish Catholic children (yes, children) were simply declared wards of the state if they missed school twice and were sent out on trains to be given away to the non catholic farmers of the Midwest as free labor. Chinese and Japanese people were mistreated badly around the time of the building of the railroads and during WW2. In coal country of Pennsylvania, 20 miners were given the death penalty because of a fake conspiracy that thought there was such a thing as the Molly Maguires. These results come from a small but effective community within the USA. Anything "other" is wrong and bad things happen because of that attitude. Trump is trumping that attitude now.
Trump is part of a global trend. Take a look at Europe today. A small number of people are flowing to Europe because of the troubles in the Middle East. While the press keeps showing pictures of people on the run, the moment is not filled with magnitude. Turkey, Lebanon, Iran, Pakistan have taken in huge numbers in comparison. Wars have always moved people around. It is at these times, when generosity is needed; the atmosphere created by people like Trump must be corrected and bent into decency for people running from harm's way. But the people are led by their politicians and when they campaign on anti-immigration, the tide is turned and the backlash is against the immigrant and their need for a new space in another land.
There was also harsh opposition to the Know Nothings, and their numbers dwindled as the country became transfixed with issues of slavery and the impending Civil War. So too, we today must be valiant in condemning the acts of the new nativists. While doing that, we must also focus on other issues that are of great importance: such as fights against inequality, the movement for black lives, and all other struggles to better the lives of our fellow man.
This kind of hate in politics has got to go. It leads to dysfunction and confusion. Trump and his ilk got to get over this nonsense. They too are immigrants. These new folks to our country are as good as or better than us.