The reactions of two key leaders sum up the dramatically different results of recent elections in Europe:

"We need to do all our best to bring in European values," said Petro Poroshenko, president-elect of embattled Ukraine.

"It's an earthquake," said French Prime Minister Manuel Valls, speaking about rejection of "European values" by populists opposed to the European Union.

This dichotomy — of Ukrainians dying during protests triggered by then-President Viktor Yanukovych reneging on an E.U. Association Agreement, while many Europeans are rejecting the postwar movement toward closer political cohesion — is yet another destabilizing dynamic that President Obama needs to respond to.

Obama, who defended his foreign policy Wednesday during a commencement address at the U.S. Military Academy, responded rightly by commending Ukrainian voters and agreeing to meet Poroshenko during his trip to Europe next week.

To be sure, Poroshenko wasn't the ideal candidate. An oligarch confectioner known as the "Chocolate King" in Ukraine, he's too close to those who've plundered the country at the expense of citizens. Poroshenko's got political baggage, too. As a longtime member of Parliament, he served in Yanukovych's cabinet before the Kremlin-friendly president fled in February after anti-government protests turned violent.

But Poroshenko got the big thing right. Unlike many enjoying the spoils of Ukraine's dysfunctional system, he stood on the right side of the protests — and history — by favoring closer association with the E.U.

Unfortunately, that institution's future is shakier after this weekend's elections. Anti-E.U. parties surged in some key countries such as Britain, where the upstart United Kingdom Independence Party (UKIP) beat the ruling Conservative Party, as well as the Labor and Liberal Democratic parties. In France, the National Front, once considered a fringe, far-right movement, moved into the political mainstream by beating the ruling Socialists, who fell to third.

While clearly conservative, UKIP and the National Front aren't openly fascist, like Greece's Golden Dawn Party, which won seats in the E.U. Parliament for the first time (as did the far-left Syriza party). Even more concerning are a few openly racist and anti-Semitic elements who have exploited European anger over immigration and unemployment.

In other countries, such as the Netherlands, Italy and Hungary, however, the center generally held. And overall the insurgency isn't strong enough — yet — to take over the E.U. Parliament. But it certainly will alter it, as well as domestic politics in many countries.

That could result in an E.U. less focused on Ukraine right when it faces a vise of Russian aggression and International Monetary Fund austerity. Russian President Vladimir Putin may have backed off a Crimean-style incursion in eastern Ukraine, but he has shown an ability and a willingness to destabilize the country, which is already facing IMF-imposed conditions for its bailout.

Frustration over Europe's economic and political sclerosis explains the "earthquake." Bureaucrats in Brussels will need to heed the message, as will leaders in multiple E.U. countries.

At the same time, however, they must not turn away from Ukraine, which longs to belong to the very same union so many Europeans are questioning, if not rejecting.

As an allied but outside leader, Obama should use his considerable clout to prod European peers to not let the anti-E.U. backlash keep them from aiding Ukraine and continue the U.S.-E.U. cohesion on punishing Russia with economic sanctions.

Failing to respond to Ukraine's time of need could create more chaos in Europe, which likely would exacerbate the economic instability that in part fuels Euroskepticism.

The E.U. and the United States have much at stake in Ukraine. If Obama and European leaders don't seize the opportunity, Putin surely will.