Why do Trump voters trust him?

Megan McArdle:

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I can see why you’d want a candidate strong on an issue you care a lot about, someone who ignores the accusations of bigotry that so often shut down serious debate on immigration. What I don’t get is why you think Trump is going to give you what you want.

After all, four years ago, the guy was an immigration liberal, criticizing Romney for taking an excessively hard line. His positions on other major conservative issues, like abortion, are shamelessly opportunistic.

His enthusiasm for bashing China is somewhat undercut by his enthusiasm for outsourcing the manufacturing of his own products to same. It’s impossible to say with certainty which way he actually leans on any issue.
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... his endlessly convenient opinion shifts, on the very core issues his supporters care most about, ought also to signal that Donald Trump doesn’t care about you, either. He’s against outsourcing and immigration, as long as that’s getting him votes. But if he can find a different coalition, he’ll happily abandon the current one in a flash.
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It is why I do not trust him on the issues he is running on.  Him immigration policy is only a more expensive version of the Gang of Eight amnesty with his round them up let them touch back in Mexico or some other country before taking them back in.  Is the vetting for that policy going to be any better than the vetting of Syrian Muslim refugees that he disdains?  His flip-flop on abortion is dizzying.  His healthcare plan is closer to Bernie Sanders than to ones favored by most Republicans.