President Trump arrives in Japan Saturday. One of the items on his agenda — as is so often the case these days — is trade. The U.S. and Japan are currently negotiating a trade agreement, discussing issues such as improving access to Japan’s agriculture markets for U.S. farmers. Japan’s auto exports to the U.S. are also a source of contention, after President Trump said last week imports from Japan and other countries are a threat to U.S. national security. He set a 180-day deadline, after which he may impose tariffs on foreign cars. To avoid such tariffs, the U.S. may look for Japan to invest more in U.S. auto production or ask it to agree to limitations on how many vehicles can come into the U.S. without an additional tariff.