The Russian occupation of eastern Ukraine produced one very hot summer. Through August, the Organization for Security and Cooperation in Europe recorded between 1,000 and 1,500 nightly cease-fire violations, a large majority committed by Russian-led forces. Ukrainian soldiers and civilians continue to be killed or injured on a daily basis. While the attacks have tailed off since Labor Day, Moscow this month teed up a huge military exercise in western Russia, Belarus and Kaliningrad that stoked fears of an even broader assault.

Since invading Ukraine three and a half years ago, President Vladimir V. Putin of Russia has mastered the tactical rheostat, turning up the heat at will, then cooling things down when the United States and Europe push back. In this way, he hopes to keep Ukraine permanently destabilized, fueling domestic discontent at Kiev’s inability to end the occupation, buying time to buy back the influence Russia lost by invading and bullying Ukraine into a Russian sphere of influence.

President Trump’s pro-Putin predilections make him the least likely answer to Ukraine’s predicament. Yet his administration is quietly fashioning a policy that just could break the ice — if Mr. Trump agrees.

It starts with a united front among Mr. Trump’s senior advisers — Vice President Mike Pence, Secretary of State Rex Tillerson, Secretary of Defense James Mattis and National Security Advisor H. R. McMaster. They see Russia’s occupation of eastern Ukraine for what it is: a gross violation of the most basic norms of international conduct that the United States helped establish after World War II. It is not acceptable for one country to change the borders of another by force. It is not O.K. for one sovereignty to dictate to another which countries or organizations it may associate with. It is not all right for Russia to decide Ukraine’s future. Mr. Trump’s team rightly believes that if the United States fails to stand against the abuse of these principles, the international order America built will be weakened.