In 2016, American liberals threatened—half seriously—that they would move somewhere more progressive if Donald Trump won the presidential election. That spring, Spotify released a tongue-in-cheek playlist called “Moving up to Canada” with the description, “Some of you might choose Canada this November … here’s the perfect soundtrack.” Now that the Supreme Court has issued the Dobbs decision overturning Roe, thus denying women the constitutional right to an abortion, the threat is back. It seems more serious and, at any rate, is much easier to carry out, because somewhere more progressive could be just across state lines, no expatriation required. The...