President Donald Trump signed a memo Thursday directing his administration to start determining what level of reciprocal tariffs the U.S. will impose on foreign imports—after long promising to announce the new round of tariffs—but the new taxes will not take effect yet.

Economists don't share Trump's enthusiasm for tariffs. They're a tax on importers that usually get passed on to consumers. But it's possible that Trump's reciprocal tariff threat could bring other countries to the table and get them to lower their own import taxes.

Logistics experts say it was impossible for major parcel carriers and USPS to overhaul their operations in a matter of days.