If your house is in Alaska, and you have a choice between closing the door and locking it, or adding insulation to the attic, which do you rationally do first to stop the invasion of cold air?
It's obvious that you start with the bigger threat to invasion and destruction of your culture, ed.
Will "they" stop? If the immigration laws are ENFORCED, a majority will stop because it will be obvious that Americans have finally decided to resist the invasion and use force to defend the border.
It also increases the economic cost for those who will still try to enter illegally, and that will stop many of them.
The majority do not have the means to enter via boat or air, and those will always be a much smaller threat IF immigration laws are enforced. However, since immigration laws are not enforced, there are a mass of people who overstay their visas, and become illegals. Enforcement is Critical. People overstay BECAUSE they CHOOSE to VIOLATE the LAW. They choose to do this because there are almost no consequences, thanks to the racist in chief (who deserves to be EXECUTED as a traitor.)
The threat from the south is also a threat to the northern European culture of the US. Canada is not.