Before the downing of a Malaysia Airlines passenger jet Thursday, much of the world chose to turn away from Russia's crimes and lies in Ukraine. Better not to look lest you have to do something. But there is no longer plausible deniability about the nature of the Putin regime. Now the question is whether we'll see a change in the world's approach to Russia—nowhere more so than by its largest business partners in the European Union.

The attack on Flight 17 has shocked people everywhere but hit closest to home in Europe. Of the 298 people aboard the Amsterdam to Kuala Lumpur flight, 211 were EU citizens, most of them Dutch. Europe's sadness has turned to anger in the days since the shootdown, as victims' bodies were left to rot in the fields of eastern Ukraine, desecrated and looted, and investigators were denied access by Russian-backed rebels.

Meantime, the Kremlin's propaganda machine pumps out reports, despite all available evidence, that the rebels didn't have advanced Russian rockets. The Kremlin media blame Ukraine and the U.S. for shooting down the Boeing BA -0.01% 777-200, even as Western governments report that Russia moved its SA-11 missile batteries back across the border into Russia after they took down the jet. This is Vladimir Putin's KGB state in action.

Such behavior should have political consequences, and the minimum good news is that the rhetoric toward Russia has changed in Europe. Dutch Prime Minister Mark Rutte said that "Putin must take responsibility vis-à-vis the rebels and show the Netherlands and the world that he is doing what is expected of him," calling the situation at the crash site "appalling."

The most outspoken Western leader has been Britain's David Cameron. At the House of Commons on Monday, the Prime Minister said if Mr. Putin doesn't stop his war on Ukraine, "then Europe and the West must fundamentally change its approach to Russia." He called France's plans to sell its Mistral naval assault ships to Russia this year "unthinkable" and called for "hard-hitting" sanctions.

"For too long there has been reluctance on the part of too many European countries to face up to the implications of what is happening in eastern Ukraine," he said, in honest self-recognition. "It is time to make our power, influence and resources felt."

Mr. Cameron's epiphany on Russia is welcome, though it's a pity he didn't find his Churchillian voice earlier in the Ukrainian crisis. He might have added that Britain has also been unwilling to pay the price of harder sanctions by cracking down on dirty Russian money flowing into the City of London. The French will need company if they're to be shamed into cancelling their $1.6 billion Mistral sale to Russia.

The Putin strategy all along has been to divide Europe from the U.S., and so far he's succeeded. A day before the crash of MH17, the EU suspended Russian access to loans from an EU-backed development bank—a pinprick sanction. Greece, Germany, Italy and the Netherlands have united to block tougher sanctions and keep the money, natural gas and luxury goods flowing.

A meeting of EU foreign ministers in Brussels on Tuesday is an opportunity to signal a new realism. The Obama Administration last week expanded the list of Russian companies and individuals that will be limited in their access to American capital markets. At the very least the EU should match those steps. But if the U.S. and Europe are serious about punishing Russia's behavior, they will tighten those restrictions to all dollar-based transactions and include other prominent companies.

The West can also "impose costs" on Mr. Putin, as President Obama keeps repeating, by targeting sectors of the Russian economy, such as finance, transportation and energy. It has threatened this move for months without action. The delay is indefensible and, in light of what happened to Flight 17, tragic. Now the policy should change to impose sanctions straightaway until Mr. Putin ends his war on Ukraine and withdraws from Crimea, not merely threatening more sanctions if the Kremlin commits some new atrocity.

Secretary of State John Kerry called the Malaysia Airlines disaster a "moment of truth" for Russia, but it's more accurate to say this of the West. Mr. Putin thinks he can escape consequences because Western leaders won't ask their constituents to make even small sacrifices to stop aggression.

Yet if Russia's aggression in Ukraine is left unchecked, sooner or later it will spread. The downing of MH17 and its aftermath offers political leaders in Europe and the U.S. a chance to educate their publics about the kind of regime Mr. Putin is running and explain what must be done to contain it before it threatens far more than innocent airline passengers.