"What we've seen with Assad and Putin is a willingness to smile at international norms and pursue power politics regardless of the cost," said Andrew Weiss, a Russia expert at the Carnegie Endowment and former official in the George H.W. Bush and Clinton administrations. "And if the West is not united and America's interests are not immediately threatened, the response immediately becomes attenuated."

How to respond has already become an issue in the 2016 presidential race. In the weeks since Putin sent Russian troops into Crimea, Republican senators Rand Paul, Ted Cruz, and Paul Ryan all criticized Obama's response. But none of them called for an American intervention in Ukraine.

Fiona Hill, a Russia expert at the Brookings Institution and a former National Intelligence Council official, said those who believed the collapse of the Soviet Union signified the triumph of Western democratic capitalism were deluding themselves. A large number of Russians remained deeply skeptical of Western norms. "It was only a very small elite around Yeltsin who were buying this," she said. "Too many people (Westerners) saw what they wanted to see, rather than what was happening."

Then the global financial crisis strengthened a perception in parts of the world that Western democracy was failing—both politically and economically, Hill added.

Shadi Hamid, a Middle East expert at the Brookings Institution's Saban Center, said Obama's decision to not intervene in Syria after last September's chemical weapons attack created a perception of American weakness. Strongmen, such as Egypt's military ruler, Abdel Fattah al-Sisi, had been emboldened. "They think they can get away with more than ever," Hamid said. "And this is tied to a growing sense of weakness under the Obama administration, whether it's fair or unfair."

Obama administration officials deny that. They argue that another costly intervention in the Middle East would further weaken the American economy. And they contend that economic and technological strength—not brute force alone—will be the dominant source of power for decades to come.

Steven Pifer, a former American ambassador to Ukraine and now a fellow at the Brookings Institution, argued that economic interconnectedness will have an impact on Putin. Pifer said the Russian leader knows he needs trade with the outside world. "While the West may rule out the military option," Pifer wrote in an email, "it has other tools, including political isolation and financial sanctions that could inflict serious pain on the Russian economy."