President Trump has described his proposal to seize control of Gaza and displace the Palestinian population as a humanitarian imperative, a gesture that would allow people living in what he called a “hellhole” to finally find peace somewhere else.

But beneath his astonishing plan were echoes of forced displacement that have shaped Palestinian society since 1948. The establishment of Israel that year in the Arab-Israeli war is known to Palestinians as the Nakba, or “catastrophe,” because of the hundreds of thousands of Palestinians who fled or were expelled from their homes.

“It’s ethnic cleansing,” said Omer Bartov, a professor of Holocaust and genocide studies at Brown University who has been critical of Israel’s conduct in the war in Gaza. Mr. Trump’s statement, he said, was “camouflaged as this humanitarian act.”

After an immediate backlash, top Trump administration officials tried to soften elements of the plan on Wednesday. They insisted that any relocation of Palestinians would be temporary and that Mr. Trump had not committed to putting U.S. troops on the ground. Mr. Trump said Tuesday that he envisioned “long-term ownership” of Gaza and that he would send troops “if necessary.”

“The president made this decision with a humanitarian heart,” Karoline Leavitt, the White House press secretary, told reporters as she stood alongside images of destruction in Gaza.

Mr. Trump had said that “everybody I’ve spoken to loves the idea of the United States owning that piece of land, developing and creating thousands of jobs.”