MOLDOVA, A small former Soviet republic in Eastern Europe, has been politically riven for years between factions seeking its integration into the European Union and other Western institutions and those who would align it with Vladi­mir Putin’s Russia. So it was shocking this past weekend when the country’s most pro-Western and pro-Putin political parties suddenly formed a governing coalition. Their stated purpose was to end the chokehold on Moldova’s institutions by an oligarch who has been accused of corrupt practices — which in Moldova, as in a number of countries across the former Soviet bloc, are a greater threat to effective government than populism, nationalism or even Putinism.

Moldova now has a fragile chance to cleanse its political system. But it will need more support than it has gotten so far from Western governments, including the Trump administration.

As of Wednesday, there was a dangerous deadlock between the new government, headed by pro-Western reformer Maia Sandu, and oligarch Vladi­mir Plahotniuc, whose Democratic Party of Moldova led the previous administration. Mr. Plahotniuc refused to recognize the new government, and justices he installed on the Constitutional Court issued a dubious ruling declaring it invalid. The court also suspended Moldova’s president and briefly replaced him with a Plahotniuc ally, who promptly ordered new elections.

This sort of ma­nipu­la­tion is exactly why Moldova’s other parties, though sharply at odds over the country’s geopolitical orientation, found it more important to jointly take on Mr. Plahotniuc. Their agreement is reportedly limited: They plan to restore independence to the court system and the national electoral commission, and reverse electoral law changes made to favor Mr. Plahotniuc. Then it would be possible to hold a new election.

If the reform succeeds, Moldova would bolster an encouraging anti-corruption wave in its region. Neighboring Romania just imprisoned its most powerful politician, Liviu Dragnea, who used his control of the previous government to change anti-corruption laws for his personal benefit. Slovakia in March elected a pro-reform president after months of popular protests against corruption. And huge demonstrations in Prague in recent weeks have demanded the ouster of Prime Minister Andrej Babis, who is dodging potential fraud charges.

Mr. Plahotniuc’s strategy for preserving his position depends heavily on convincing Washington that he is pro-Western. His D.C. lobbyists portray him as anti-Russian, even though he just tried to strike a deal with the pro-Putin Socialists. On Tuesday, desperate to gain favor with the Trump administration, the rival government he backs announced it would move the Moldovan Embassy in Israel to Jerusalem and provide a prime piece of property for a new U.S. Embassy.

The Trump administration shouldn’t be fooled by such tactics. So far the State Department has struck a cautious position, urging that the results of the last parliamentary election be respected. Leading E.U. states, including Britain, France and Germany, have gone further by fully endorsing the new anti-corruption coalition. The United States should join them.

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