On April 2, Trump introduced Reciprocal tariffs. So question now, on May 29th, is whether these are legal. Whether Trump can in fact impose these kinds of tariffs.
The argument put forward by the administration roughly consists of two parts as explained by Matt Levine (here1, here2, here3). The first is that the ability to impose tariffs follows from the ability to regulate imports. Under this premise, the legality of the tariffs is then “reduced” to the legality over whether Trump can regulate imports.
The ability to regulate imports appears to be specified by the International Emergency Economic Powers Act which says that (1) there is an unusual and extraordinary threat to the U.S. economy whose origination (or source) comes from outside the U.S. and (2) the President declares a national emergency with respect to such a threat, then the President can regulate imports.
So the argument, put forward by the administration, appears to boil down to whether a trade deficit constitutes an unusual and extraordinary threat to the U.S. economy, whose source comes from outside the U.S.
