Donald Trump this week pivoted to embrace a niche constituency that few would have expected him to champion—cryptocurrencies and the deep-pocketed investors who have made them their domain. The former president and onetime bitcoin skeptic on Monday helped launch a new crypto business with his family. On Wednesday, he bought a round of burgers for denizens of a bitcoin-theme dive bar in New York. Pledges to block a Federal Reserve-backed digital currency and establish a “strategic national...