Egypt has stepped up its military presence in the Sinai Peninsula since Oct. 7, 2023, in apparent violation of its peace treaty with Israel. Recently, photos have circulated of rows of tanks in the desert. They aren’t there to confront Israel, which would pound Egypt in any military confrontation. The threat Cairo sees emanates from the Gaza Strip, where Egypt is determined to keep its border closed to refugees.

That puts Cairo at odds with U.S. policy. President Trump has offered a bold vision for allowing Gazans to resettle elsewhere and ultimately redeveloping the strip. But unless Gazans have a means of escape, Hamas will continue to use them as human shields and cannon fodder.

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With great chutzpah, President Abdel Fattah Al Sisi is using U.S. aid to thwart U.S. policy. Egypt is America’s second-largest regular military aid recipient. Israel is first, but the $1.5 billion Cairo receives makes up nearly a quarter of its military budget. U.S. assistance to both countries flows from the 1979 Camp David Accords. Thus American taxpayers are paying to hold an iron curtain down on Gaza and maintain a status quo of war and oppression.

Mr. Trump’s plan for reconstructing Gaza is premised on allowing the population to flee the territory for a better life elsewhere. The humanitarian need for this is urgent. This week’s renewal of large-scale hostilities after a failed cease-fire will inevitably entail the dislocation of many Gazans. That isn’t Israel’s goal, which is to rescue hostages and destroy Hamas. But it’s what happens in wartime.

The flight of refugees across borders is also a regular consequence of war. Six million Syrians—nearly a quarter of the prewar population—fled their country during its civil war. Even more have left Ukraine, even though most of the country’s territory is free from active hostilities. More than 1.5 million people have fled Afghanistan since the Taliban’s takeover in 2021. Yet since Oct. 7, Egypt has locked virtually all of Gaza’s population in place.

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Forty-four percent of young Gazans wanted to emigrate before the war, according to public-opinion polls. Neighboring Egypt is an Arab country that professes concern for Gazans. International refugee law obligates Egypt to provide asylum to at least a significant number of Gazans. Cairo bears heavy responsibility for Hamas’s atrocities, having allowed it to construct massive smuggling tunnels across the border since Israel’s withdrawal in 2005.

Egypt did so to destabilize the Jewish state, whose repeated trouncing of Egypt’s army is a point of national shame. Cairo, which brutally occupied Gaza from 1948-67, continues to play a spoiler in the territory. A thriving Gaza of the kind Mr. Trump envisions would, like Israel, be a humiliating counterpoint to the poverty of Egypt.

Barack Obama froze aid for two years after Mr. Sisi took power in a coup. But the Egyptian leader seems not to take Mr. Trump and his aspirations for the region seriously. Can Mr. Sisi take for granted that Mr. Trump will keep the dollars flowing?