Russia is an even tougher country to pressure, too formidable even in the post-Soviet age to rattle with stern lectures or shows of military force, and too rich in resources to squeeze economically in the short term. With a veto on the United Nations Security Council, it need not worry about the world body. And as the primary source of natural gas to much of Europe, it holds a trump card over many American allies.

The longer-term options might be more painful, but they require trade-offs as well. The administration could impose the same sort of banking sanctions that have choked Iran’s economy. And yet Europe, with its more substantial economic ties, could be reluctant to go along, and Mr. Obama may be leery of pulling the trigger on such a potent financial weapon, especially when he needs Russian cooperation on Syria and Iran.

“What can we do?” asked Fiona Hill, a Brookings Institution scholar who was the government’s top intelligence officer on Russia during the Georgia war when Mr. Putin deflected Western agitation. “We’ll talk about sanctions. We’ll talk about red lines. We’ll basically drive ourselves into a frenzy. And he’ll stand back and just watch it. He just knows that none of the rest of us want a war.”

James F. Jeffrey was Mr. Bush’s deputy national security adviser in August 2008, the first to inform him that Russian troops were moving into Georgia in response to what the Kremlin called Georgian aggression against South Ossetia. As it happened, the clash also took place at Olympic time; Mr. Bush and Mr. Putin were both in Beijing for the Summer Games.

Mr. Bush confronted Mr. Putin to no avail, then ordered American ships to the region and provided a military transport to return home Georgian troops on duty in Iraq. He sent humanitarian aid on a military aircraft, assuming that Russia would be loath to attack the capital of Tbilisi with American military personnel present. Mr. Bush also suspended a pending civilian nuclear agreement, and NATO suspended military contacts.

“We did a lot but in the end there was not that much that you could do,” Mr. Jeffrey recalled.

Inside the Bush administration, there was discussion of more robust action, like bombing the Roki Tunnel to block Russian troops or providing Georgia with Stinger antiaircraft missiles. Secretary of State Condoleezza Rice bristled at what she called the “chest beating,” and the national security adviser, Stephen J. Hadley, urged the president to poll his team to see if anyone recommended sending American troops.

None did, and Mr. Bush was not willing to risk escalation. While Russia stopped short of moving into Tbilisi, it secured the effective independence of South Ossetia and Abkhazia, while leaving troops in areas it was supposed to evacuate under a cease-fire. Within a year or so, Russia’s isolation was over. Mr. Obama took office and tried to improve relations. NATO resumed military contacts in 2009, and the United States revived the civilian nuclear agreement in 2010.