The most important borders for Americans to worry about are our own. But the downing of Malaysian Airlines Flight 17 has certainly shifted media attention from the crisis on our southern border to the borders of Ukraine. Although we do not know with certainty, it appears likely that pro-Russian rebels were the ones who shot down the airliner, killing nearly 300 innocent civilians. The rebels have downed several Ukrainian airplanes, including military transports. The rebels do not have an air force of their own, so it is they, not the Ukrainians, who have been shooting at aircraft. The Malaysian airliner was flying from west to east, so it likely appeared to the rebels to be another Ukrainian plane. Indeed, there are intercepted conversations among the pro-Russian rebels discussing the downing of the airliner, and one rebel group briefly took credit for shooting down a plane, until it became clear that it was a civilian airliner. Not even Russia is suggesting that Ukraine downed the airliner, though reasonable questions have been raised about Ukrainian air traffic control and why the airliner was flying over what has become the scene of a low level civil war.
If the pro-Russian rebels did shoot down the airliner, the pressure will build on Vladimir Putin to definitively distance himself from them. It is hard to say that the pressure will be misplaced. Russia recognized Ukraine as an independent country following the collapse of the Soviet Union, and Russia agreed to uphold Ukraine's sovereignty in exchange for Ukraine's giving up the nuclear weapons it inherited from the Soviet Union in 1994. Putin may lament the collapse of the Soviet Union as a "geopolitical disaster," but the real disaster would result from any attempt to resurrect the Soviet Union or even the Russian Empire. (Putin has been trading off misplaced nostalgia for the Soviet Union for some time, and even told a Russian veteran on D-Day that he was open to renaming Volgograd "Stalingrad.")
Most Ukrainians do not want to be part of Russia's "near abroad." In this they resemble most Poles, Estonians, Latvians, Lithuanians, Finns, Czechs, Slovaks, and Hungarians. Those who experienced Russian rule, either under the tsars or the commissars, generally do not harbor any nostalgia for it. Instead, they fear its return. A post-Communist Russia does not pose any threat to us, and the United States should stay out of Russia's dispute with Ukraine for that reason. But Russia does pose a potential threat to its neighbors, and giving support to rebels who shoot down airliners will do nothing to reassure those worried by a revival of Russian power. Putin's task should be to allay the fears of Russia's neighbors, not to stoke them.