WASHINGTON, March 18 (Reuters) - President Donald Trump's administration is considering deploying thousands of U.S. troops to reinforce its operation in the Middle East, as the U.S. military prepares for possible next steps in its campaign against Iran, said a U.S. official and three people familiar with the matter.The deployments could help provide Trump with additional options as he weighs expanding U.S. operations, with the Iran war well into its third week.Those options include securing safe passage for oil tankers through the Strait of Hormuz, a mission that would be accomplished primarily through air and naval forces, the sources said....