Demographic change has been a hallmark of what is now the United States, even before the area was the United States and even before Europeans settlers arrived. This is nothing new.
Before European explorers and settlers arrived, Iroquoian Nations, such as the Five Nations (later the "Six Nations:" the "Iroquois") and the Huron Confederations, began to impinge on the established Algonquin tribes in western New England, southern New York and in the Ohio Valley in the 16th Century.
Access to steel-bladed weapons and firearms after the arrival of French, Dutch and, later, English/British settlers allowed the Five Nations to expand its footprint at the expense of Algonquin tribes like the Delaware and the Mohicans and Iroquoian rivals like the Huron, the Erie and the Neutral nations (the latter two decimated) in the Beaver Wars over control of the fur trade in the 17th Century.
Relatedly during this period, the British displaced the Swedes in what is now Delaware and the Dutch in New York and New Jersey.
Within the next approximately 100 years, particularly from 1697 to 1763, the British were able to displace the French from North America. This lead to population displacement, such as French settlers from Arcadia in what is now the Canadian Maritimes being transported to French Louisiana to become the ancestors of today’s Cajuns.
Between 1763 and 1776, attempts on the part of the Crown to reconcile the conflicting needs and interests of former French Colonists and French allied tribes in the former New France, existing British colonists in the 13 Colonies and traditional British allied tribes (such as the Five Nations and the Cherokee) was a major source of friction between the Crown and the 13 Colonies.
Before and after the American Revolution, the immigration of disloyal, primitive and tribal Highland Scots, grasping and avaricious Lowland Scots, and the swaggering, violent and disputatious Ulster Scots/Scots Irish was a major source of disruption . . . as was these groups’ relative success as compared to established settlers. The various Scots groups would do work (such as working as itinerant peddlers and stoop laborers) and settle in places (on the Frontier) more reasonable people (or those with better options) would not.
Additionally, many of the Highlanders were Papist and most of the other Scots were non-conformists, outside the scope of either the Anglican “Broad Church’ or the established Congregationalist Churches of New England.
Initially, they were Presbyterian, but the lack of resources on the Frontier drove them into the arms of other nonconformist denominations (such as the Baptists) that put less stock in the academic background of the clergy and more on their zeal, ability to preach and devotion to the Bible. Other nonconforming groups joined them like the Society of Friends in Pennsylvania and the Methodists as that movement grew out of the Broad Church in the 18th Century.
These events provide a template for the effects of the immigration of others like Christian and Jewish Germans, mere Irish, Eastern and Southern European Christians, Eastern European Jews, Lebanese, Armenians and Syrians, Mexicans and others in the mid to late 19th Century and early 20th Century.
New arrivals are resented due to their low status, differing cultures and . . . eventual economic success. It was true 242 years ago and it is true today.
It was unquestionably a factor in Trump’s election in 2016, as demonstrated by some of Trump’s more fringe supporters chanting ”You will not replace us” when they marched through Charlottesville, VA a few years ago. However, American History indicates that newer group tends to "replace" (or at least amalgamate with) older groups, usually to everyone's ultimate benefit.
Although illegal immigration was the issue Trump's Campaign seized upon, perhaps noting the uproar that sank the "Gang of Eight" Immigration Reform Compromisee in 2007 and Immigration Reform in 2013, it is worth noting that the illegal immigrant population was stable during the period when Mr. Trump launched his campaign and that the number coming from Mexico was declining.
It is also worth noting that, while Sen. Obama supported the legislation in 2007 and President Obama supported 2013 legislation (and attempted to implement part of it by Executive Order), he was not a major factor either time. In fact, both major parties' triangulation while trying to court the growing Hispanic voting population while trying to placate existing stakeholders (the white working class for Republicans, the Union Hierarchies for the Democrats) seemed to lead to the election of Trump as surely as Grenville and North's Government's attempts to balance competing interests in British North America had lead to the American Revolution after 1763.
While Mexicans still constituted the largest number of illegal immigrants (and the number of Central American illegal immigrants was increasing), a Wall on the Mexican Border hardly seemed an immigration panacea. This seemed especially true given the fact that this approach does not address the issue of people over-staying their Visas, a large source of the problem.
This issue has gptten a lot of attention from those attempting to understand the roots of the Trump Presidency. However, it was not the biggest factor in Mr. Trump's election.