SHANGHAI—The last time Washington mobilized for a trade war, Ronald Reagan was president and Japan the adversary.

Today, the White House is readying the same big guns—a mix of tariffs and quotas—aimed mainly at Chinese imports. It has in its sights everything from steel to solar panels and washing machines. A record Chinese annual trade surplus with the U.S., announced last week, is the potential catalyst for hostilities after a year of bluster from President Donald Trump.

A trade war isn’t a certainty, but if it comes, it will look nothing like the battles that raged in the 1980s over Japanese semiconductors, cars and TV sets.

The forces are more evenly matched this time: America has never faced off in a trade skirmish with an opponent like China in terms of economic size, industrial capabilities and global ambitions.

Japan was a U.S. ally, China increasingly a rival. That raises the risk of tit-for-tat escalation, especially since support for Beijing is crumbling across the U.S. political spectrum as well as in the U.S. business community, traditionally a strong advocate for China trade.