I agree with your use of "trumpkin." It is a very important distinction. Their anti-immigrant positions are not held by conservatives or traditional republicans. See the CATO institute, the Bushes, McCain, McConnell, Romney, and Ryan. The core conservative actors all support immigration. They know how valuable immigration is to our industries and economy.
The alt-right, Steve Bannon, Donald Trump, and Steve Miller wing of the party are leading the charge against immigrant for the trumpkins.
Racism applies. Xenophobia and nativism may be more accurate.
The MS-13 stories, stories of crimes by "illegals," and false and overblown economic impact stories are all obvious propaganda trying to tap into nativism. Fox news is full of this.
Humans evolved into families and tribes so these urges can be very strong. Unfortunately, the biggest counter to nativism and xenophobia are education, life experiences with new people, and traveling to new places. This is why the republican party is susceptible.