WASHINGTON—President Donald Trump welcomed Saudi Arabia’s Crown Prince Mohammed bin Salman to the Oval Office on Tuesday by showcasing photographs of tanks and helicopters that the U.S. has sold the Middle East kingdom to help it build up its military muscle.

Across town, senators debating a contentious proposal meant to curb American military support for Saudi Arabia were shown a sobering image of a Yemeni toddler injured by an airstrike, one victim of Riyadh’s protracted war against Iran-backed militants.

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