Vladimir Putin’s annexation of Crimea is a direct challenge and long-term threat to the post-World War II international order for which the United States and our allies have made great sacrifices over the past seven decades.If Putin is allowed to take land from a neighboring nation through deceit and raw military force without serious consequences, the precedent could have global repercussions, including in Asia.While it is best to avoid conflict whenever possible, history shows that illegitimate aggressions that go unchallenged are a virtual guarantee of even more dangerous conflict in the future.Fortunately, Putin’s illegitimate actions have united the United States and its allies in the free world in opposition. But while the steps taken so far by President Barack Obama and the United States’ European allies are welcome, they clearly will not be enough in the face of a determined Russian effort to forcibly redraw Europe’s borders. Putin’s annexation of Crimea must be met with immediate and meaningful consequences for his regime and those who benefit from it.First, U.S. financial leverage toward Russia should be used to greater effect. We should work with our partners in Europe to launch an asset-recovery program to identify the spoils of the Russian regime’s corruption, which often are hidden abroad.Second, we need to diplomatically isolate Russia, removing them immediately from every international forum not essential to resolving this crisis, including the Group of Eight. The NATO-Russia Council should be dissolved. Put simply, Russia should no longer be considered a responsible partner on any major international issue. The Russian people should see that Putin’s actions will bring about a decline of Russia’s status as a global power, not a return to supposed Soviet glory.Obama should urge U.S. allies to impose an arms embargo on Russia. It is unconscionable that NATO allies would send arms to Moscow even as it violates Ukrainian sovereignty.Third, I welcome the fact that Vice President Joe Biden has visited the region to bring a message of reassurance to our allies and partners. I hope those assurances include a specific and clear response to requests by Georgia and Ukraine for lethal military support from the United States. We also need to deploy additional military assets and even U.S. personnel to our allies, including Poland and the Baltic states.Fourth, the Russian invasion of Crimea should dispel the myth that closing NATO’s door to future allies would appease Russian aggression. We must make clear to all interested partners in Europe who wish to join NATO and meet the requirements that the alliance remains open for membership. The president has sufficient tools at his disposal to do most of these things. But his hand would be strengthened if a united Congress gave him the necessary authority to follow through. I hope that events this past week and Russia’s unrelenting aggression will lead Congress to move quickly to pass an assistance package to Ukraine and tough sanctions on Russia. Although I remain concerned by the proposed International Monetary Fund reforms included in the legislation, the need to send a strong bipartisan message of solidarity to the people of Ukraine and a statement of resolve to Moscow far outweighs any misgivings I and others might have. Marco Rubio, a Republican from Florida, is a member of the Senate Foreign Relations Committee and the Senate Select Committee on Intelligence.