“My initial reaction — Putin must be jumping for joy,” said Marcus Kolga, a Canadian-Estonian filmmaker and activist who advocates a tough line with Moscow. The “timing and nature of this is extremely alarming.”

Senior figures in Mr. Roivas’s center-right Reform Party, which now does not have enough seats left to govern on its own, acknowledge they will be discussing his resignation on Tuesday morning in a meeting before the vote, expected later in the day.

The immediate cause of the coalition’s split was a dispute over appointments of lawmakers to the boards of state companies. But it also occurred right after the downfall of a political boss, Edgar Savisaar, a former prime minister who lost his place last weekend as the leader of the Center Party after more than two decades.

“He was the last guy, the remnant of that first generation who led Estonia since the regaining of independence” from the Soviet Union, said Lauri Tankler, a journalist and political commentator, who was in the United States covering the American election for the Estonian public broadcaster ERR.

The Center Party’s links to Russia had put off potential partners, but without Mr. Savisaar, the smaller parties may see a chance to escape the orbit of the Reform Party, which has been a mainstay in every Estonian government since 1999. And Mr. Savisaar’s newly elected successor as chairman, Juri Ratas, in particular appears to strike a markedly less favorable tone toward Moscow, and without the baggage of corruption accusations that had weighed down Mr. Savisaar.