By Steve Holland
WASHINGTON, March 3 (Reuters) - With Russia's incursion into Ukraine reviving Cold War-style tensions, President Barack Obama is at risk of suffering a blow to his credibility at a time when he can least afford it: as he tries to convince voters to stick with his fellow Democrats in congressional elections that will help shape his legacy.
For five years, Obama has practiced a cautious approach to foreign policy crises, prizing sober diplomacy and the search for consensus over brinkmanship, in prolonged conflicts in Iraq and Afghanistan.
But the deliberative style that Obama's team sees as a statesmanlike attitude in tune with Americans' war-weariness, was described as dithering in the crisis over Syria, where the United States long discussed military action without committing.
Facing his toughest test yet in Ukraine, Obama is once again finding himself portrayed as a weak leader, outmaneuvered by a wily, opportunistic Russian President Vladimir Putin intent on reviving the United States' nemesis.
His popularity has already been suffering because of the disastrous roll out of his signature healthcare plan last October and the U.S. economy's slow recovery from recession.
Now, Republicans are using Ukraine as further ammunition against him ahead of the November elections.
The Ukraine crisis, said Republican Senator John McCain in a speech on Monday, is "the ultimate result of a feckless foreign policy where nobody believes in America's strengths anymore."
It's not only Republicans who are giving less than rave reviews to Obama's strategy. The Washington Post's lead editorial on Monday was about Obama and Ukraine and was entitled "The risks of wishful thinking."
"For five years President Obama has led a foreign policy based more on how he thinks the world should operate than on reality," it said.
Obama seemed to have been caught off-guard by Putin's seizure of the Crimea region of southern Ukraine. He is now scrambling to put together a package of economic sanctions aimed at isolating Russia.
Targeted asset freezes against key Russian officials are a possibility. A G8 summit that Obama and allies are to attend in Sochi, Russia, in June is on hold.
"Obviously, the facts on the ground in Crimea are deeply troubling and Russia has a large army that borders Ukraine. But what is also true is that over time this will be a costly proposition for Russia," Obama said on Monday.
This will not be enough to satisfy critics who fear Putin is taking a step toward restoring the old Soviet Union that he served as a KGB colonel. Putin's adventure in Ukraine, they say, is the final proof that Obama's policy of resetting U.S. relations with Russia in a search for common ground is dead.
For Obama, the Ukraine crisis is a dramatic diversion from attempts to stay focused largely on domestic affairs in a congressional election year that may represent his last best chance for legacy-building achievements before Americans look past him and focus on the 2016 presidential campaign.
The president and fellow Democrats are struggling to hang on to control of the Senate and build up their numbers in the Republican-controlled House of Representatives in November elections.
In addition to using the Ukraine crisis as another cudgel against Democrats in this year's congressional elections, Republicans also see it a possible line of attack in the 2016 presidential race. Some potential Republican White House hopefuls, such as Florida Senator Marco Rubio, have been pushing a more assertive foreign-policy approach.
"The president must now accept that the only way to deal with tyrants like Vladimir Putin is with a clear understanding that they can't be trusted and that only decisive action will deter their provocative moves," Rubio said.
White House officials frequently point out that Obama's more cautious approach is in sync Americans' weariness of foreign wars.
"He has a leadership style for foreign policy consistent with what the American people want to see done in the world today," said Mike McCurry, a former State Department and White House spokesman for President Bill Clinton. "That kind of severely limits the posture you can have for robust foreign policy when the American people really want us to pull back."
In the case of Ukraine, White House officials say, Obama's actions are already hurting Russia because the threat of sanctions has rattled financial markets there and undermined Putin's attempt to buff the image of Russia after having hosted the Sochi Winter Olympics.
"We're already seeing Russia pay a real cost for its actions in Ukraine," White House deputy national security adviser Tony Blinken told CNN. "All this is undermining how Putin defines his power."
This is what Thomas Alan Schwartz, a presidential historian at Vanderbilt University, calls "an international shaming of Putin, trying to make it seem like Putin is on the wrong side of history."
McCain said this won't be enough. The Republican senator has been sharply critical of Putin and first raised the issue of Ukraine in a 2008 presidential debate as he ran against Obama.
McCain now says the United States should respond to Putin's move in Ukraine by bolstering military ties with the Baltic nations, Estonia, Lithuania and Latvia, and welcome Georgia as a NATO member. (Additional reporting by Mark Felsenthal and Thomas Ferraro; Editing by Caren Bohan and Peter Henderson)