Nobody knows how much longer Ukraine's status as an independent nation will continue, but Russian President Vladimir Putin has put himself in position to be the decisive factor on the issue. He has done so despite the protests of the weakest American chief executive since Jimmy Carter was president during the Russian invasion of Afghanistan in 1979.

For Carter, the sight of Russian tanks rolling into Afghanistan was a wakeup call. He reversed some of the ill-advised defense decisions he had made and took the crucial first steps in the U.S. defense buildup that President Reagan wisely continued and expanded. Reagan's policies ultimately led to the collapse of the Soviet Union, the end of the Cold War and the creation of an American military capable of protecting U.S. interests around the world.

Now Putin is moving aggressively as Obama fritters away Reagan's efforts. Once again, a democracy is being forced to re-learn that brutal regimes must be dealt with from a position of strength. Obama's reliance on a diplomatic “reset” with Russia was tragically misguided, willfully ignorant of Neville Chamberlain's belief that a piece of paper signed by Hitler assured “peace in our time.”

To be sure, Obama's severely limited options aren't entirely of his own making. He inherited a military and a public wearied by the wars in Iraq and Afghanistan, and an economy hobbled by the Great Recession of 2008. But rather than being honest with the American people about the need to rebuild the U.S. military to cope with a resurgent Russia and an ever more aggressive China, Obama did the opposite, offering instead the false promises of diplomacy and Pentagon downsizing.

As Senate Armed Services Committee member Jim Inhofe of Oklahoma said: “I warned this day was coming, and it is here. President Obama's attempt to seek peace through apologetic diplomacy while defunding and dismantling our military has failed. Today, our enemies don't fear us and our allies no longer respect us.”

What now? The world can only hope that Putin's occupation of Crimea will have the same sobering effect on Obama as Carter experienced in 1979. If it does, Obama will stop drawing red lines that nobody respects and begin the difficult process of rebuilding American military might. As for Ukraine, Obama’s response must be taken with a view not merely to stopping the aggression in the Crimean peninsula but to inflicting economic pain that will make Putin think twice before launching another military adventure.

The key Russian economic leverage is energy, particularly natural gas. Obama should ask Congress immediately to remove the ban on exporting U.S. oil and natural gas to European markets. All arms control negotiations with Russia should be suspended and the G-8 summit cancelled. The U.S. assets of the Russian oligarchy should be frozen. Then Obama should make clear that there will be no more apologies.