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The Trump campaign’s post yesterday about the “Third World” went beyond Trump’s known obsession with migrant crime to highlight an embrace of the “Great Replacement” theory.

Karen Lewis, a therapist in Washington, D.C., talks with a lot of frustrated single people—and she likes to propose that they try a thought exercise.
Imagine you look into a crystal ball. You see that you’ll find your dream partner in, say, 10 years—but not before then. What would you do with that intervening time, freed of the onus to look for love?
I’d finally be able to relax, she often hears. I’d do all the things I’ve been waiting to do.

A basic fact of thermodynamics is coming to haunt every foot of train track in the United States. Heat makes steel expand, moving its molecules farther apart, and as hot days become hotter and more frequent, rail lines are at risk of warping and buckling more often.
Any fix must deal with this fundamental truth of physics. Railroads can slow their trains down, which avoids adding more heat.

The first time Angel Giuffria saw the logo on her bionic hand, she felt a sense of pride. She was born without the lower half of her left arm, and started wearing a prosthesis at six weeks old. Back then, it had a beige cover—a design that was meant to mimic skin, but looked obviously fake. This new hand abandoned any unsettling attempt at imitation. Instead, it had a Star Wars–like aesthetic. Giuffria was delighted.