President Joe Biden is not planning to answer a further Russian invasion of Ukraine by sending combat troops. But he could pursue a range of less dramatic yet still risky military options, including supporting a post-invasion Ukrainian resistance.
The rationale for not directly joining a Russia-Ukraine war is simple. The United States has no treaty obligation to Ukraine, and war with Russia would be an enormous gamble, given its potential for expanding in Europe destabilizing the region, and escalating to the frightening point of risking a nuclear exchange.
