WASHINGTON As the bloodiest day of anti-government protests in Ukraine was drawing to a close last month, U.S. Vice President Joe Biden called President Viktor Yanukovich for the second time in three days and delivered a blunt message.
Pull back your security forces now and accept a European-brokered settlement or you will be held accountable, Biden warned the pro-Russian leader. "It WILL catch up with you."
Initially defiant, Yanukovich sounded subdued by the end of the hour-long call, according to a senior U.S. official knowledgeable of the conversation. Within hours, Yanukovich signed a deal with the opposition and then fled to Russia.
Whether Biden's 11th-hour warning was decisive or merely served in a supporting role to European Union negotiators, his intensive telephone diplomacy illustrates the kind of troubleshooting that has become integral to his portfolio in President Barack Obama's second term.
However, given the United States' limited options in the Ukraine crisis after Russia seized the Crimea peninsula, Biden's role as a loyal Obama adviser on foreign policy poses risks to his political future if he runs for president in 2016.
Biden would be unable to separate himself from the administration's record on Ukraine if the West comes out on the losing end of its worst standoff with Moscow since the Cold War.
"He's tied to Ukraine policy, no matter how it comes out, said Shirley Anne Warshaw, a presidential scholar at Gettysburg College in Pennsylvania. "So he could be vulnerable."
Republican critics can also be expected to keep the heat on the administration - and by extension, Biden - for what they say is a foreign policy that has exposed U.S. weakness in issues like the Syrian civil war, Iran nuclear talks, Afghanistan and the growing military challenge from China.
Possible 2016 Democratic rival Hillary Clinton decided to stake out a hawkish stance on Russian President Vladimir Putin last week. In condemning Moscow's Crimea incursion, she invoked Adolf Hitler's actions leading up to World War Two.
Though Clinton said she was not making a direct comparison between the two men, the former secretary of state's line of attack was at odds with the White House's more cautious approach and made her look tough on Russia as she considers a possible presidential campaign.
GETTING IT MOSTLY WRONG - OR NOT
Biden made a name for himself early in his Senate career as a centrist Democrat calling on his party to be more willing to back diplomacy with power. But since taking office, Biden, mindful of Americans' war-weariness, has often been in sync with Obama's reluctance to commit to new armed entanglements.
Former Defense Secretary Bob Gates put Biden on the spot when he wrote in his memoir released in January that the vice president, over the past four decades, had been "wrong on nearly every major foreign policy and national security issue" - areas long viewed as his strengths.
Republican Senator John McCain said Gates' critique had merit, telling CNN that Biden "has been wrong on a lot of these issues." McCain has since blamed the administration's "feckless" foreign policy for inviting the Ukraine crisis.
Biden's supporters see Gates' accusation as an attempt to settle scores. "The vice president argued that we shouldn't put as many troops in Afghanistan as they (the Pentagon) wanted," said Ted Kaufman, Biden's longtime chief aide before being appointed to serve out his term as Delaware's U.S. senator. "Joe was right."
As Biden eyes a possible White House bid, another unpopular war could still weigh on his decision. Though he spearheaded administration policy that brought about the U.S. withdrawal from Iraq, he failed to secure a deal to keep a modest troop presence there.
Even years later, an issue that would likely resurface in a presidential campaign is an often-ridiculed proposal he made as head of the Senate Foreign Relations Committee that essentially advocated splitting Iraq in three along sectarian lines.
Biden could also have to answer questions about the advice he famously gave to Obama in 2011 not to go ahead with the raid in Pakistan that killed Osama bin Laden. The vice president has admitted he thought the special forces operation was too risky.
The ability to act as outspoken contrarian in the inner circle was one of Obama's chief reasons for picking Biden. He also brought vast congressional experience in foreign policy and personal relationships with a who's who of world leaders.
Biden's old-school, back-slapping style - and occasional verbal gaffes - makes him the opposite of the cool, deliberative Obama. But what he won from Obama was a promise to allow him to be the last voice in the room, associates say.
Biden has leveraged his role to avoid the vice presidential curse of irrelevance, which was widely seen as the plight of Al Gore, the last Democrat to hold the office. But Biden has also steered clear of the behind-the-scenes power games of his immediate predecessor, Republican Dick Cheney.
"Biden has found a way to be influential on foreign policy without feeling the need to claim his own turf," said Warshaw, author of the book "The Co-Presidency of Bush and Cheney."
After five years, Biden's role appears to be that of tending to some of Obama's toughest problems - going to "places that he doesn't want to go," as the vice president told a Munich security conference only half-jokingly in 2013.
But some supporters privately wonder whether, as he gets closer to a decision on 2016, he may want to start easing himself out of Obama's shadow, especially on foreign policy.
For now, Biden's fortunes could hinge to an extent on what happens with Ukraine and its former Cold War master, Russia.
It was Biden, in fact, who was credited with coining the phrase "push the reset button," the administration's early - and since abandoned - approach to Russia.
Republican critics point to Crimea as final proof that the "reset" was naïve, and they can be expected to try to use it as ammunition against Democrats in this year's mid-term elections and against Biden if he seeks the presidency two years later.
But Clinton might also be vulnerable as she too promoted the reset policy, which did yield a nuclear arms control pact, a deal for U.S. forces to use Russian territory going to and from Afghanistan and Russian cooperation on Iran sanctions.
In any presidential campaign, Clinton would also face questions about how she handled the 2012 killing of four Americans, including the U.S. ambassador, in a militant attack in Benghazi, Libya.
TASKED WITH CRISIS MANAGEMENT
Tony Blinken, Biden's national security adviser during the first term, insisted the vice president was "always clear-eyed" about the "reset" outreach to Moscow and rejected from the outset any Russian "sphere of influence" encompassing ex-Soviet republics.
As protests erupted in Ukraine in November after Yanukovich spurned a free trade deal with the EU for closer ties with Russia, Obama tasked Biden to be his main point of contact with the Ukrainian leader. Biden had first met Yanukovich, then opposition leader, during a visit to Ukraine in 2009.
Speaking to Yanukovich half a dozen times as the crisis escalated, Biden urged him not to make "the classic mistake of coming in with too little, too late" to meet protesters' grievances, the senior administration official said.
In their final call on February 20, with dozens already killed in Kiev's Maidan square, Biden warned Yanukovich that if he went ahead with an even more violent response, "it won't just be history that judges you" but the Ukrainian people. Russia's operation in Crimea began within days of Yanukovich's flight.
Even as Secretary of State John Kerry has taken the role of trying to get Russia to back down, Biden remains a key player. He cut short a trip to Latin America to attend Obama's talks on Wednesday with Ukrainian Prime Minister Arseniy Yatseniuk.
"He has been and will be at the center of our policy," said Blinken, now Obama's deputy national security adviser.
(Reporting by Matt Spetalnick; Editing by Tom Brown)