Donald Trump is leading the field for the 2016 Republican presidential nomination by a wide margin. Of his policy positions, nothing has distinguished his campaign more than his ultra hard-line immigration proposals. These two facts are mostly undisputed, but so far commentators have focused on how both a Trump presidency and the imposition of such strict border controls are unfeasible. It’s a good way to avoid reckoning with their substance and consequences. When we’re talking about millions of lives at risk, however, it pays to be mentally prepared.In order to “make America great again,” Trump wants first to better define it. Candidate Trump, if elected, plans to build a wall around the country. He also wants Mexico to pay for the construction costs. It’s a ridiculous, albeit somewhat popular, project, but the wall deflects attention from the rest of his dead-serious immigration plan.Trump has accumulated a lot of support from the GOP nativist base in large part because they trust him to enforce immigration laws. The first sentence in his plan is “When politicians talk about ‘immigration reform’ they mean: amnesty, cheap labor and open borders,” and he’s right. Few national politicians and fewer business leaders are serious about deporting 11 million people. Undocumented immigrants are a necessary part of the national economy; American enforcement practices are designed to manage, not eliminate, violations of border laws.