VILNIUS, Lithuania — Vice President Joseph R. Biden Jr. found himself in a fraught but familiar place this week: holding the hands of American allies fearful of being bullied by a larger, aggressive neighbor.
This time, it was Poland and the Baltic states, rattled by Russia’s move to annex Crimea and its potential designs on the rest of Ukraine. Three months ago, it was Japan and South Korea, unnerved by China’s sudden imposition of an air defense zone in the East China Sea.
The cases differ in obvious respects: The tensions in Asia have eased somewhat after the Chinese government showed prudence in policing its air defense zone, while in Europe, the confrontation with Russia over Crimea seems to be only escalating.
But there are also striking parallels: Russia and China are both ambitious powers, riding a tide of nationalism and nursing grievances over historical slights at the hands of the West.
Continue reading the main storyAnd both are led by self-confident strongmen — Vladimir V. Putin and Xi Jinping — though the popularly elected Mr. Putin may have a tighter grip on his society than the Communist Party boss, Mr. Xi, who must contend with an independent-minded military.Both may be exploiting a belief that the United States is turning inward, exhausted by years of war and reluctant to get drawn into costly foreign entanglements.
For President Obama, deciphering the motives, means and next moves of these suspicious giants will require a mix of psychology and geopolitics. Kremlinology and Sinology may end up as the major foreign policy preoccupations of the remainder of his presidency.
So far, the administration’s response to the threats has been similar: to emphasize the ironclad treaty commitment of the United States to its allies and to offer measured displays of force: sending a pair of B-52 bombers to fly through the contested Chinese airspace; giving the Baltic states 10 more fighter jets to patrol their skies.
“We stand resolutely with our Baltic allies in support of the Ukrainian people and against Russian aggression,”Mr. Biden said after meeting in Vilnius, the capital of Lithuania, with the country’s president, Dalia Grybauskaite, and President Andris Berzins of Latvia.
“As long as Russia continues on this dark path, they will face increasing economic and political isolation,” he said.
For now, administration officials say, Russia presents a harder case than China. Mr. Putin has been brazen in his takeover of Crimea and troubling in his assertion that Russia will protect Russian-speaking populations in the nations that ring his country, while Mr. Xi has only inched forward with Beijing’s territorial claims in the South and East China Seas.
Russia has shrugged off European and American sanctions and ridiculed assertions that it is flouting international law, while China appeared to heed widespread condemnation and Mr. Biden’s show of solidarity with American allies after it imposed its air defense zone.
China has yet to impose a second such zone over the South China Sea, as many in the region had predicted it would. American military commanders say the Chinese Air Force has been prudent in patrolling the zone, allaying fears of a miscalculation if Chinese fighter jets were scrambled to intercept a Japanese plane flying through it.
None of this is to suggest that the tensions in Asia have ebbed. A simmering confrontation between China and the Philippines in the South China Sea flared up recently when Chinese ships turned away Philippine ships trying to deliver supplies to a small military detachment.
American officials still live in fear that China will land troops on the Senkaku Islands, which it claims under the name Diaoyu Islands, but which are controlled by Japan. The United States would be obligated by treaty terms to defend Japan in a military clash with China. And the concerns about China’s muscle-flexing are not limited to these islands.
“China’s military is expanding dramatically, creating concern for a host of American allies,” said Ian Bremmer, founder of the Eurasia Group, a political risk consultancy. He said he viewed China as a greater threat than Russia, “and by a very large margin.”
The United States can draw comfort from the fact that Mr. Xi’s overriding goal, experts say, is to maintain stability outside China’s borders so he can manage a host of problems at home, including a slowing economy and tensions over official corruption.
Indeed, China has expressed qualms about Mr. Putin’s adventurism. Normally a stalwart ally of Russia in the United Nations, it declined on Saturday to oppose a Security Council resolution rejecting the referendum for secession in Crimea, abstaining instead.
For all of Mr. Putin’s bluster, some experts doubt that he would risk a wider conflict.
“Putin is also rational and respects U.S. power,” said R. Nicholas Burns, a former under secretary of state who teaches at Harvard. “It is very unlikely he would threaten a NATO ally such as Estonia, Latvia or Poland due to NATO’s security guarantee.”
Mr. Burns said the president should draw clear red lines with Russia and China and show that the United States is prepared to defend its treaty obligations. That was the main purpose of Mr. Biden’s visit this week, with his mantra-like repetition of Article V, the clause of the NATO treaty that commits members to regard an armed attack on any one of them to be an attack on all.
It is also worth remembering, Mr. Bremmer said, that Russia has been losing influence steadily for 20 years, “demographically, diplomatically, economically and militarily.”
Mr. Putin’s actions, he said, are evidence more of insecurity than of strength.
Robert Danin, a senior fellow at the Council on Foreign Relations, said: “Russia is a traditional military power sitting atop a declining economic and industrial base. In contrast, China is a military power rooted in a strong and growing economic foundation.”
That may explain why Mr. Obama, after meeting with European allies in Brussels next week, will travel a month later to Asia. There, he will follow in Mr. Biden’s footsteps with a tour of China’s anxious neighbors: Japan, South Korea, Malaysia and the Philippines.