If Viktor Yanukovich, the winner of the presidential race in Ukraine, acts quickly to address his country’s pressing problems, he could move it out of the doldrums and cure the “Ukraine fatigue” afflicting Washington and most European capitals.

As Viktor Yushchenko exits the presidency, Ukraine faces a host of problems. It suffered a crushing 14 percent fall in gross domestic product in 2009. Unwise pricing policies and widespread corruption have put the critical gas sector in virtual bankruptcy. The nasty in-fighting between Mr. Yushchenko and his prime minister, Yulia Tymoshenko, kept Kiev from implementing needed responses to these challenges.

As a result, Ukraine fatigue has again gripped the West. This malady first broke out in 1998 in the U.S. Congress. American legislators, weary of the slow pace of reform and mistreatment of U.S. investors, scaled back their generous assistance earmarks for Kiev. A subsequent outbreak was cured by the 2004 Orange Revolution, as Ukrainians inspired the West with a determined defense of their right to have their votes counted fairly.

Unfortunately, Mr. Yushchenko and Ms. Tymoshenko, close allies during the Orange Revolution, could not cooperate in power and failed to build on the revolution’s promise. Ukraine fatigue returned with a vengeance. The country has ceased to be a priority for the European Union and, given everything now on the Obama foreign policy plate, barely registers on Washington’s radar.

Mr. Yanukovich’s victory on Sunday rings with irony. After all, the Orange Revolution threw out his tainted election. But the Ukrainian electorate has given him a new chance. He now has an opportunity — and the responsibility — to show he can provide the decisive leadership his country needs.

Whatever the preferences might have been in the Washington and Europe, Ukrainians have made their choice. No compelling evidence of major voting irregularities has emerged, and international observers praised the election for meeting democratic standards, now the norm for Ukraine. The West should congratulate and engage Mr. Yanukovich, and urge him to get on with addressing Ukraine’s daunting problems.

A serious attack on corruption would create better conditions for both Ukrainian and foreign businesses. Reforming the gas sector would strengthen Ukraine’s energy security and benefit Europe: Gas spats between Kiev and Moscow have twice in the past four years halted gas flows to Europe. Coherent policymaking in Kiev would give Western capitals something with which to work.

Tackling this reform agenda will require tough decisions by Ukraine’s new leadership. The United States and European Union should jointly send a message to Kiev containing three key points:

First, the West welcomes Mr. Yanukovich as the democratically elected leader of Ukraine. However, a reversal of the democratic progress that Kiev has made in the past five years would have profoundly negative consequences for relations with the West.

Second, the West understands that Mr. Yanukovich’s foreign policy may differ from his predecessor’s. The doors to integration and cooperation with institutions such as the European Union and NATO nevertheless will remain open; Kiev should indicate how far and how fast it wishes to proceed.

Third, the West will assess his seriousness by the seriousness of his policies. The West cannot want Ukraine to succeed more than Ukrainians do. Should Mr. Yanukovich avoid crucial actions such as energy sector reform, that is his choice — even an understandable one given the tough politics that surround the issue. The West will still seek good relations. But Washington and Brussels should make clear that in such circumstances, Kiev should not expect the West to extend itself by intervening, for example, with the International Monetary Fund to cut Ukraine slack on meeting its loan obligations.

The goal should be to encourage Kiev to take steps that will make Ukraine more democratic, more stable and more capable of fending for itself. That will advance the country’s interests and make it a better partner for Europe. If Kiev proves unwilling to take such steps, the county will linger in the doldrums — and Ukraine fatigue in the West will grow.