The writer was U.S. national security adviser from 2005 to 2009.

The shooting down of Malaysia Airlines Flight MH17 has focused the world’s attention on Russian-backed separatists in eastern Ukraine. But the most basic questions are still unanswered: What is Russian President Vladi­mir Putin up to? How far will he go? And what should the United States do about it?

Putin ordered the invasion of Georgia in 2008, the invasion and annexation of Crimea in 2014, and now the destabilization of eastern Ukraine. In so doing, he has shredded the post-Cold War settlement in Europe embraced by all European nations (including Russia) after the collapse of communism and the end of the Soviet Union: acceptance of existing borders, the sovereignty and territorial integrity of all states, and the right of all states to choose their affiliations free from the threat or use of force.

What does Putin want? He has a different vision for Europe. He seeks the restoration of Russian greatness through a Russian-dominated confederation of states (the “Eurasian Union”), along with associated trade and security organizations. He is shrewd, strategic and patient. He has Belarus, Kazakhstan and Russia as members, with Armenia, Kyrgyzstan and Tajikistan waiting in the wings.

But Putin needs Ukraine to give his project economic and geopolitical heft. That requires preventing Ukraine from joining the European Union and NATO. By annexing Crimea and provoking secessionists in eastern Ukraine, Putin accomplishes two things. He pressures Ukraine. And he creates the kind of territorial dispute with Russia that will make European states loath to accept Ukraine as a member of NATO or the E.U.

The objective of coordinated U.S. and E.U. sanctions should be to convince Putin to withdraw Russian weapons and mercenaries from Ukraine and end cross-border support to the secessionists. The Ukrainian government can then start the autonomy talks with its eastern citizens that it wants to pursue — and that Russia says it seeks — but that the Russian presence and support for secessionists make impossible. Such talks can pave the way for the Ukrainian government to address its citizens in Crimea about their concerns and status. That dialogue must also be free from Russian coercion.

But are sanctions enough? No. Putin has been adept at exploiting division and disruption among Russia’s neighbors to advance his goals. The United States needs to:

●Deny Russia targets of opportunity by eliminating or hardening Europe’s vulnerabilities against Russian exploitation.

●Reassure NATO allies vulnerable to Russian pressure that NATO stands by its Article 5 guarantee of their security.

●Deter further Russian action against Ukraine or any other state in violation of the basic principles of the post-Cold War settlement.

●Avoid the redivision of Europe that would follow the exclusion of Russia from Europe at variance with its historical and economic ties to its neighbors to its West.

Why this latter point? Putin’s actions have been reprehensible. But the door must be left open to a Russia that returns to the post-Cold War consensus — either because of a change of heart by Putin (however unlikely) or because of efforts by those Russians committed to a more peaceful and democratic future.

How to achieve these objectives? The United States working with the European Union needs a comprehensive strategy that takes these actions:

●Reenergizes the historic vision of a Europe whole, free and at peace as an alternative to Putin’s vision of Russian domination of its neighbors and increasing authoritarianism at home.

●Completes the Transatlantic Trade and Investment Partnership binding Europe and the United States in a relationship of economic growth and prosperity, leaving the door open to adding additional participants such as Turkey and, ultimately, a peaceful and democratic Russia.

●Develops a joint transatlantic energy strategy using liquid natural gas shipments from the United States, shale oil and shale gas produced in Europe, creative use of existing pipeline infrastructure and construction of new non-Russian controlled pipelines to reduce the E.U.’s dependence on Russian oil and gas.

●Resumes the E.U.’s “open door” policy of offering association agreements and, ultimately, membership to countries to the east that seek them with arrangements that do not require severing historical and economic ties to Russia.

●Recommits the United States to the security of Europe through additional military deployments and exercises.

●Revitalizes the NATO alliance through additional planning, exercises and military capabilities for the organization’s core mission of European security and with an open door to states seeking membership who meet its criteria.

●Helps nations subject to Russian pressure to strengthen their capacity to defend their territories from either armed attack or subversion and destabilization, including by providing military, paramilitary and police training and equipment.

●Helps the Ukrainian people overcome two decades of failed leadership and build an inclusive, democratic and honest government and market-based economy.

How far will Putin go? If history is any guide, he will push forward as long as he has success and does not meet serious resistance. To stop him requires not just sanctions but all the elements of a comprehensive strategy.