RIO DE JANEIRO — Venezuela, which a decade ago aspired to be the axis of a new, left-leaning diplomatic and trade alliance in the Americas, is finding itself increasingly isolated in the hemisphere.

Venezuela downgraded diplomatic relations with Canada and Brazil in recent days, after a war of words over the Venezuelan government’s decision last week to ban three influential opposition parties from running candidates in next year’s presidential election.

As its leftist president, Nicolás Maduro, is increasingly regarded as a despot among neighbors in a region that has shifted politically to the right, Venezuela, once the richest country in South America but now in need of cash, is drawing closer — and becoming more dependent on — Russia and China. With its oil, Venezuela is likely to be an attractive, if risky, long-term gamble for Moscow and Beijing, which have sought in recent years to assert greater influence in a region that Washington has long regarded as its backyard.

“Marginalizing the Venezuelan kleptocracy is important, but total isolation will cede the ability of regional leaders to shape political events on the ground to actors outside the region,” said Juan Gonzalez, a former White House and State Department official in the Obama administration who worked on Latin America policy. “Russia’s increased role is particularly concerning, given their proven interference in the 2016 U.S. election and apparent design to disrupt regional politics.”