The International Longshoremen’s Association strike is shaping up as a test of the president’s mettle on the eve of the election. The effort to shut down the ports and block American commerce is the kind of union overreach that, in 1947, led the GOP-controlled Congress, over President Truman’s veto, to enact the Taft-Hartley Act. That law would allow President Biden to reopen the ports while negotiations go on — if he has the aforementioned mettle.