During the 2012 presidential election, Mitt Romney declared that Russia had become the United States’ “number one geopolitical foe,” a comment that the Democrats used at the time to paint him as inept. Although his remark was a gaffe reeking of overstatement, it may not have been completely wrong, given Russia’s recent invasion of Ukraine.

The former Soviet state has faced turmoil since November, when Viktor Yanukovych, the former president, announced that he would stop negotiating with the European Union to strengthen trade agreements. Pro-EU Ukrainians, who claimed that Yanukovych was the Russian government’s puppet, marched in the streets. After months of periodic bloodshed, during which government snipers massacred protesters, Ukraine’s parliament voted to oust Yanukovych. Fleeing to Russia to avoid a warrant for his arrest, he claimed that he was the sole legitimate ruler of the country.

However, not everyone supports the removal of Yanukovych and Ukraine’s new government. Counter-protests erupted in Crimea, a semi-autonomous eastern part of Ukraine, resulting from the repeal of a law allowing Russian to be used as a minority language there. The majority of Crimeans speak Russian and align themselves culturally and linguistically with Russia, unlike the people of western Ukraine, who speak Ukrainian and identify themselves more closely to Western Europe.

To add to the complexity of the conflict, Russia has violated Ukraine’s sovereignty, deploying troops in Crimea in what it claims is an attempt to defend Russian speakers.

Why would Vladimir Putin, Russia’s president, decide that sending 6,000 troops into Ukraine would be a good idea? It isn’t an easy question to answer: Fareed Zakaria, an international affairs expert and editor for Time Magazine, calculates that Putin made a huge mistake.

His analysis of the situation is spot-on. For the decision to flex its muscles against a country that spends one-eighteenth the amount that it does on its military, Russia will draw the ire of the international community. Canada has already withdrawn its ambassador from Russia. World powers are reconsidering Russia’s status in the G8, a forum of the most powerful countries. Russia’s agenda in the United Nations, which has been to veto any objective the U.S. tries to pass, may be less popular. It could face harsh sanctions from the European Union, the U.S. and other countries that will probably reevaluate their relationships with Russia.

What should the U.S. do? Some interventionists may be eager to intercede militarily on the behalf of Ukrainian sovereignty, but this would be a terrible choice, one that the U.S. is highly unlikely to make at this point. If the situation changes and Russia invades the rest of the country, the U.S. should demand the U.N. act in order to defend Ukraine. However, if the situation does not escalate further and Russian troops don’t fire on Ukrainians, the U.S. government should seek harsh sanctions against Russia, including asset freezing and trade disruptions, and consider removing its ambassador.

The U.S. government’s response to Russia should be strong and swift. Not acting in Syria, which may have been seen as a sign of weakness, could have led Putin to believe that he could get away with an invasion of Crimea. The U.S. must demonstrate that Russia has no business there, even if Crimeans no longer want to be a part of Ukraine. Ukrainians must determine their country’s future without any foreign influence, Russian or European.