Immigration in essence is an issue that hinges on race. White conservatives vote on race. As Michael Tesler, a political scientist at the University of California at Irvine, put it in The Washington Post in November 2016:
Racial attitudes became strongly connected to whether whites identified as Democratic or Republican during Barack Obama’s presidency. That, by itself, meant that racial attitudes would matter a great deal in 2016 — even above the powerful impact of partisanship itself.