Barely a week ago, Israelis rallied in Tel Aviv’s Hostage Square, waving placards thanking President Trump and his Middle East envoy for their role in helping secure an initial cease-fire deal in Gaza and getting some hostages freed.

Many of them were hoping that Mr. Trump would strong-arm Israel’s long-hesitant prime minister, Benjamin Netanyahu, into agreeing to negotiate an end to the war with Hamas and get the rest of the hostages released when the two leaders met in Washington on Tuesday.

Instead, they woke up to news of Mr. Trump’s fantastical idea of removing the population of roughly two million Gazans from the devastated enclave to make way for a glittering, American-owned Middle Eastern Riviera.

Far-fetched as Mr. Trump’s vision for Gaza may be — the Arab world has roundly rejected it and any forcible removal of a population violates international law — it abruptly shifted attention away from the future of the cease-fire deal, whose initial, six-week phase is due to end in early March.

As Mr. Trump sketched out his grandiose plans for Gaza, he placed little public pressure on Mr. Netanyahu to proceed with talks via Qatari and Egyptian mediators to turn the temporary cease-fire into a permanent cessation of hostilities. That left Israel with a wide berth on how it might deal with Gaza next.

The talks, which were meant to start this week, are now up in the air. And Mr. Netanyahu will leave Washington with Mr. Trump’s endorsement of what far-right members of the Israeli government have effectively been calling for: the mass migration of Palestinians from Gaza.