WASHINGTON—As President Trump and his top aides weighed a military operation against Iran in early June, Vice President JD Vance and Secretary of State Marco Rubio wanted to ensure that American troops wouldn’t end up entangled indefinitely in another Middle East war.Gen. Dan Caine, the newly confirmed chairman of the Joint Chiefs of Staff, shared the concern of others in the room about putting Americans in harm’s way. He pulled out a map in the Situation Room and explained how, if ordered to link icon=none linkend=https://www.wsj.com/world/middle-east/trump-gave-final-go-ahead-for-iran-attack-hours-before-bombs-fell-17df9dc4 type=EXTERNALstrike Iran’s nuclear facilities/link, the Pentagon could protect the pilots involved in the mission and defend U.S. troops in the Middle East from any Iranian retaliation.