President Trump basked as Prime Minister Benjamin Netanyahu of Israel praised his “willingness to think outside the box.” But when it came to Gaza, Mr. Trump’s thinking on Tuesday was so far outside the box that it was not clear he even knew there was a box.

Mr. Trump’s announcement that he intends to seize control of Gaza, displace the Palestinian population and turn the coastal enclave into “the Riviera of the Middle East” was the kind of thing he might have said to get a rise on “The Howard Stern Show” a decade or two ago. Provocative, intriguing, outlandish, outrageous — and not at all presidential.

But now in his sequel term in the White House, Mr. Trump is advancing ever-more brazen ideas about redrawing the map of the world in the tradition of 19th-century imperialism. First there was buying Greenland, then annexing Canada, reclaiming the Panama Canal and renaming the Gulf of Mexico. And now he envisions taking over a devastated war zone in the Middle East that no other American president would want.

Never mind that he could name no legal authority that would permit the United States to unilaterally assert control over someone else’s territory or that the forcible removal of an entire population would be a violation of international law. Never mind that resettling 2 million Palestinians would be a gargantuan logistical and financial challenge, not to mention politically explosive. Never mind that it would surely require many thousands of U.S. troops and possibly trigger more violent conflict.

Mr. Trump’s idea would be the most expansive commitment of American might and treasure in the Middle East since the invasion and reconstruction of Iraq two decades ago. And it would be a jaw-dropping reversal for a president who first ran for office in 2016 decrying nation-building and vowing to extract the United States out of the Middle East.

“This is literally the most incomprehensible policy proposal I have ever heard from an American president,” said Andrew Miller, a former Middle East policy adviser under Presidents Barack Obama and Joseph R. Biden Jr. and now a senior fellow at the Center for American Progress.

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