> given that the U.S. Constitution grants the government the sole power to coin money Not true. It grants Congress the power to coin money (Article I §8 ¶5), a

> given that the U.S. Constitution grants the government the sole power to coin money Not true. It grants Congress the power to coin money (Article I §8 ¶5), and prohibits the states from doing the same (§10 ¶1), but it says nothing about private citizens. Coins can legally exist which were not created by Congress or by any state. Arcade tokens would be one obvious example. In any case "to coin money" refers specifically to making coins, as in physically stamping them out of metal. Whether or not they're treated as "currency" in a legal sense, cryptocurrencies are obviously not physical coins so rules about coining money do not apply. From a tax perspective, the special treatment applied to foreign currencies is a result of specific treaty obligations. It only applies to small amounts of income—under $200 IIRC—and is meant to avoid the need to report small fluctuations in value when you hold foreign currencies temporarily for travel. In other respects the rules are the same as for cryptocurrencies, or really any other kind of property apart from USD. It's not surprising that the currency rules are not applied to something like Bitcoin which we have no treaties about and whose use is not strongly correlated with travel outside the country.