In Paris, as a political novice facing a powerful master of geopolitical intrigue, Mr. Zelensky had few cards to play without Americans in his corner. With the United States, he would have a patron who could keep Ukraine in the fight and who controlled the one weapon the Kremlin feared — sanctions imposed on Russia for its attacks on Ukraine and seizure of Crimea.

The United States has never been a formal participant in the Minsk process. But many officials advised its government and kept the American government informed about the complex state of play. Many of them were the cast of characters in the impeachment hearings — Kurt Volker, the former special envoy to the peace process; Marie Yovanovitch, the former ambassador to Kyiv; and Fiona Hill, the former adviser on Europe and Russia at the White House. They have all left their posts. Only William Taylor Jr., the acting ambassador to Kyiv, is still active, but after being dismissed as a “Never Trumper” by the president, his words carry little weight.

Testimony shows they all had been sidetracked by a president who favored Mr. Putin over the Ukrainians, saw support for Ukraine as merely the price for political favors and limited his efforts to free Ukraine from Russian aggression to telling Mr. Zelensky, during a meeting at the United Nations in September, “I really hope you and President Putin get together and can solve your problem.”

But the problem is something Mr. Putin has no interest in solving except on his terms, which include keeping Ukraine clear of the European Union and NATO so that it remains under Russian influence. Even Ukraine itself is deeply divided over how to resolve the crisis. Nationalists see any negotiations with Russia as capitulation, while Mr. Zelensky was elected with the support of those who hoped he could find a way to end a conflict that has already taken 13,000 lives.

Mr. Trump’s disdain for Ukraine was further on display Tuesday when he invited Russia’s foreign minister, Sergey Lavrov, to the White House for what the president tweeted was a “very good meeting” — a Russian cabinet official getting a meeting that Mr. Trump had denied to the president of Ukraine. They met on the day House Democrats announced articles of impeachment based on his manipulation of Ukraine — not one of the six topics of discussion he listed in his tweet.