President-elect Donald Trump has said many negative things about cryptocurrencies. Their value is “based on thin air,” he remarked; they can “facilitate unlawful behavior.” Bitcoin “seems like a scam,” he told Fox Business in 2021. “I don’t like it because it’s another currency competing against the dollar.” Things change. This year, Mr. Trump proposed that “if bitcoin is going to the moon, I want America to be the nation that leads the way.”