President Trump has long reveled in his reputation as a maximalist, issuing a huge demand, creating a crisis and setting off a high-pressure negotiation.

But increasingly often, he ends up backing down and simply declaring a win. His opponents appear to be catching on, sharpening their tactics based on Mr. Trump’s patterns and his unapologetically transactional attitude toward diplomacy.

The dynamic has played out repeatedly in recent weeks as Mr. Trump backed off, to varying degrees, on his plans to transform Gaza into the “Riviera of the Middle East,” turn Canada into the 51st state and beat China into submission with tariffs.

Now, two very different tests are emerging. One is over where Mr. Trump stands, with America’s biggest allies or with President Vladimir V. Putin of Russia, on preserving Ukraine’s sovereignty and safety in any cease-fire deal. The other, with Iran, may determine whether he is really willing to stand aside and let Israel bomb Iran — or join in, despite the risks — if he cannot extract a better nuclear deal than what President Barack Obama got, and cut off Iran’s pathway to a bomb.

Both those negotiations lack the numeric symmetries of tariff negotiations. Thousands if not millions of lives are potentially at stake. Both involve decades of grievance, dating back to the Iranian revolution and the breakup of the Soviet Union.

And Russia and Iran appear to be honing their strategies after watching Mr. Trump in action. Emissaries from those countries are hinting to Mr. Trump’s negotiator, Steve Witkoff, that there may be some investment opportunities for Americans if the United States eases off its demands. Mr. Witkoff, like Mr. Trump, has a history in real estate.