As Donald Trump prepares to fulfill a lengthy list of campaign promises, the president-elect’s vow to ensure that all remaining Bitcoin is “made in the USA” may prove to be one of the most challenging to keep.

Bitcoin is made through a process known as mining, in which operations use high-powered, fuel hungry computers to solve complicated math problems used to validate transactions in the network and post them to a public ledger,

A technology expert on Thursday took aim at one of President-elect Donald Trump’s many campaign promises for when he sweeps back into office next month: his vow that all remaining Bitcoin be “made in the U.