When it comes to confronting global conflicts, President Trump is a man in a hurry.

Even before his inauguration, the president claimed credit for what he called an “EPIC cease-fire” in Gaza. He has raced to get Ukraine and Russia to quickly embrace a pause in fighting. And with Iran, Mr. Trump wants an agreement within two months to prevent Tehran from developing a nuclear weapon.

It is the foreign policy version of the president’s “flood the zone” approach in Washington, where he and his lieutenants have used blitzkrieg-like tactics to dismantle the bureaucracy, consolidate executive power and attack his political enemies. On the world stage, too, Mr. Trump has embraced a hurry-up foreign policy approach designed to quickly resolve the disputes he inherited.

But his diplomatic impatience is now running headfirst into the complexity of war and peace, raising questions about the durability of what he has achieved so far. The cease-fire between Gaza and Israel has collapsed. Mr. Trump’s proposal for an immediate 30-day cease-fire was rejected by President Vladimir V. Putin of Russia. And an Iran nuclear agreement — not unlike the one he withdrew from during his first term in office — seems to remain far over the horizon despite his push for a speedy deal.

“Trump’s MO is to always be in a hurry, looking for the transaction, for the temporary, for the now,” said Aaron David Miller, a former Middle East negotiator and a fellow at the Carnegie Endowment for International Peace.

“American foreign policy — Ukraine, Gaza, Iran — they’re not measured in terms of administrations. It’s generational time,” Mr. Miller said. He added that rushing a solution was risky, “because he’s in such a hurry to get results, he’s sort of misdiagnosing the problem.”