The GOP establishment likes open borders because its big corporate donors want cheap labor. (The Democratic establishment likes open borders because immigrants usually vote Democratic.) But many ordinary Americans — mostly, but not at all exclusively, Republicans — wonder what's in it for them. More immigrants means more competition for jobs, pushing wages down, whether it's at entry-level unskilled jobs, or at the higher-level tech jobs where employers abuse H1B visas to bring in cheap foreign labor.For us non-oligarchs, the cheap labor prized by big GOP donors is just unwanted competition in the labor markets. Their interests and ours, if not diametrically opposed, are at least in conflict. They, however, pay the piper and call plenty of tunes, hence Jeb Bush's fabulous fund-raising.
Most GOP pols won't touch this issue, which pairs the risk of scaring off immigration-dependent donors with the added danger of being called racist by Democrats. Trump doesn't care, so he is willing to raise the issue anyway. And he has done so effectively.
Meanwhile my nephew, drawing a six figure salary, is just about the only non-Indian in his IT unit in CA. Talk about H1B abuse. It is a real thing.