China. Iran. North Korea. Venezuela. Foreign-Policy Tests Mount for Trump.

President Trump’s “America First” foreign policy is being challenged on four fronts at once, creating an extraordinary test of the White House’s ability to manage multiple crises and deliver on its ambitious agenda.

In Asia, China is seeking to renegotiate the terms of yearslong trade talks. North Korea is again testing short-range missiles, with talks over Pyongyang’s nuclear forces stalled.

In the Middle East, Iran is threatening to ramp up its nuclear program and, according to U.S. intelligence, has prepared to attack American forces. In Latin America, Venezuela has thwarted...