US immigration policy has deeply racist roots. From his rhetoric to his policies, President Donald Trump has continued this tradition, most notoriously through his border wall, migrant family separation, and child detention measures. But who exactly supports these practices and what factors drive their opinions? Our research reveals that racial attitudes are fundamental to understanding who backs the president's most punitive immigration policies. We find that whites who feel culturally threatened by Latinos, who harbor racially resentful sentiments, and who fear a future in which the United States will be a majority-minority country, are among the most likely to support Trump's actions on immigration. We argue that while the President's policies are unpopular with the majority of Americans, Trump has grounded his political agenda and 2020 reelection bid on his ability to politically mobilize the most racially conservative segment of whites who back his draconian immigration enforcement measures.