The invasion of Ukraine by Russian President Vladimir Putin is a watershed in European history. It may also become the defining moment for the presidency of Barack ObamaBarack Hussein ObamaTop nuclear policy appointee removed from Pentagon post: report Prosecutors face legal challenges over obstruction charge in Capitol riot cases Biden makes early gains eroding Trump's environmental legacy MORE. Unfortunately, Obama's response to the crisis in Crimea has been more disappointing than presidential. Obama has failed to provide the personal priority, urgency, and multinational effort necessary to resolve this pivotal crisis. The best way to deal with Putin's power grab is for Obama to meet within 48 hours in Warsaw with the other leaders of NATO to announce united action against Russia.

This would send the right message to the American people, our allies, Ukraine, and Russia. First, it would communicate that this crisis is receiving the highest priority of the President of the United States. There is a broad sense in the United States and across the world that Putin's invasion of Ukraine is Obama's Cuban missile crisis. Anything less than Obama's personal leadership in the international community's response to the Ukraine crisis will show lack of commitment to both Putin and our allies. It will fail to deter Putin and weaken the trust of our friends, especially those closest to Russia's military aggression.

This is why the emergency meeting of NATO heads of state should be held in Warsaw. It will show the countries in Central Europe that the US and all of NATO stand by them when the danger of conventional warfare in Europe is greater than it has been since 1989. Putin's use of force to seize Ukrainian territory has shattered the post-Cold War peace in Europe. Our allies and partners in the region need reassurance that American and NATO commitments remain strong. It would be a grave mistake to underestimate the need to provide such reassurance at this critical time in history.

Thus, Obama's trip to Warsaw will manifest strong US leadership in response to Russian aggression in Ukraine and help address security concerns within the region. Choosing to address those security concerns with our NATO allies will also communicate that Putin faces a united West. By acting together, the US, Canada, and our European allies will increase the power of deterrence and decrease the danger of the conflict spreading.

At the Warsaw meeting, NATO leaders should agree to take clear and prompt actions to raise the costs of Russian occupation of Crimea. This should include significant economic sanctions against Russia. Also, instead of not attending the next G-8 meeting in Russia in June, the NATO members of the G-8 (together with Japan) should end the G-8 relationship with Russia and henceforth meet only as the G-7, as they did previously. The NATO members of the WTO should also announce their decision to work together to expel Russia from that organization.

In addition to these diplomatic and economic steps, the leaders of the Alliance should also deploy the NATO Response Force (NRF) to eastern Poland. The NRF was created precisely for such crisis management missions and Putin has made Ukraine the most dangerous crisis in Europe since the fall of the Berlin Wall. It is important that the leaders of NATO not settle for just voicing concern/condemnation for Russia's use of force in Ukraine. Russia and the world need to see the US and our allies respond collectively to Putin's invasion with tangible actions, not just diplomatic communiqués.

Obama and the leaders of NATO need to take these important actions together to match the historic change in European security that occurred when Russian troops began seizing Ukrainian territory. An emergency NATO summit in Warsaw will send the right message of reassurance and deterrence that both friends and foes need to hear. Obama should seize the opportunity to lead this summit and leave a legacy of dealing with this crisis by acting promptly, decisively, and with strong international support.

Benitez is the director of NATOSource and a senior fellow at the Atlantic Council.