Ten or 15 years ago, Friedrich Merz would have seemed a wildly unlikely candidate for the role of savior to Europe’s liberal democracy. Spoiler alert: He still does. But the internal decay of European politics has reached a critical stage, whose stakes were made abundantly clear by the ludicrous spectacle of Donald Trump and JD Vance berating Volodymyr Zelenskyy in the Oval Office for insufficiently groveling before the Orange Throne. This was not the historical moment Merz expected, and it definitely isn’t the one he wanted. But for better or worse, he looks to be Europe’s last man standing. If...