A political newcomer whose anti-corruption pledges won him the presidency of Ukraine in a landslide could weaken Russian President Vladimir Putin, Western officials say.

Both Russia and Ukraine have been dominated by wealthy oligarchs since the collapse of the Soviet Union. If newly-minted Ukrainian President Volodymyr Zelenskiy can corral the tycoons, the officials believe, it would embarrass Putin and pressure him to allow reforms in his own country.

“If he shows progress, Russian citizens would demand for their own government to change,” a European diplomat, speaking on the condition of anonymity, predicted to the Washington Examiner.

An American official was even more emphatic. “I think he is an existential threat to the Putin regime,” the official, who was not authorized to speak publicly, concurred.

The Trump administration is positioning itself to help Zelenskiy, a 41 year-old former comedian and actor who won the April elections with 73% of the vote. Trump signed a letter inviting him to Washington for a state visit last week, just days after his inauguration. The former actor and comedian has stoked misgivings by hiring advisers who could be a bad influence on his anti-corruption agenda, but the Trump administration sees his presidency as an opening to blunt Russian efforts to dominate Ukraine.

“The future of Ukraine over the next five years is going to be determined in the next three months,” Special Representative Kurt Volker, the State Department’s point man for the crisis in Ukraine, told the Washington Examiner.

The coming weeks are so crucial because Zelenskiy has sky-high popularity, but the legislature is dominated by his rivals. And, Western officials are troubled that he has at least one major oligarch friend. Zelenskiy has tapped a lawyer associated with Ihor Kolomoisky — the internationally-disdained founder of a bank that was nationalized in 2016 after receiving a multibillion-dollar bailout amid allegations of fraud and mismanagement — as his chief of staff.

On the other hand, Kolomoisky also bankrolled a private militia that blunted Russia’s territorial gains in 2014, and backed Zelenskiy’s campaign. But the relationship feeds into skepticism that Zelenskiy will provide the kind of return on investment that Trump will seek from a political partnership.

“Is the U.S. going to ratchet up its support for Zelenskiy or not?” asked Donald Jensen, a senior adjunct fellow at the Center for European Policy Analysis. “It depends on the extent to which Zelenskiy can convince the administration that he's aggressively pushing economic reform.”

Zelenskiy is trying to assure the European Union and the United States that he has a sincere intention of reforming Ukraine and that Western powers have a stake in his success.

"Ukraine in the EU is the death of the Russian imperial project,” he said Wednesday. “Moreover, it is a powerful blow against Russian authoritarianism, it is the path to democratic change in Russia and the whole post-Soviet space.”

Russia annexed Crimea and invaded eastern Ukraine with unmarked forces in 2014 in an effort to stop the former Soviet vassal state from strengthening relations with the European Union. The conflict sent U.S.-Russian relations into a nosedive. A pair of cease-fire agreements provided only partial relief from the fighting, which Russia still portrays as an internal civil war.

Zelenskiy campaigned on ending the war, but Putin responded to Zelenskiy’s win by offering Russian passports to Ukrainians who live in territory controlled by Moscow, maintaining that the two countries are “one people” and ought to have “common citizenship.”

In fact, Ukrainian public opinion has turned sharply against Russia since the war began. But the historic affinity between the two societies is a key part of the reason that reform in Ukraine could be so troublesome for Putin.

“This is another model for the Slavic world,” said the other U.S. official, who was not authorized to speak publicly. “If they can reform in Ukraine, people are going to be like, 'why can't we do that?’"

Volker is doing what he can to stir the pot. He has touted publicly the idea of having the Ukrainian government work with the European Union to implement antitrust legislation that would pressure the oligarchs to relinquish control of major industries for amnesty from prosecution and a financial clean bill of health.

“If you want to fix corruption, fix the oligarchic system so that you reintroduce competition across the entire economy,” Volker said.

The Trump administration isn’t insisting on that specific idea, however, and Zelenskiy will have to gauge what kind of reforms he can call for during the elections. Jensen thinks that he’s “probably not” capable of winning a legislative majority without logistical help from his oligarch friend, and Ukraine has no shortage of other power brokers likely to see the parliamentary elections as an opportunity to advance their interests.

“There are influences behind the scenes with lots of money that are very important,” Volker observed. "And it's not only Kolomoisky, by the way. He's got lots of people who will try to do this. And, he's got to be the one to try to fight against that and be as successful as he can be.”