President Biden has been battling a new phenomenon in American politics: what Democrats and pollsters have taken to calling “Trump amnesia,” a softening of feeling about his predecessor’s tumultuous term as president. But over roughly 24 hours on Tuesday, Donald J. Trump provided what looked like at least a temporary cure. He reposted a video containing the words “unified Reich,” reviving accusations that he flirts with Nazism. He hinted at the idea of restricting contraception, and rehired as a campaign aide a political operative with a record of accusations of sexual harassment. A court ruling unsealed later in the day...