WASHINGTON -- When Secretary of State John Kerry was scrambling last week to prevent the leader of the Syrian opposition from boycotting a meeting with him in Rome -- a snub that could have spoiled his maiden voyage as the nation's chief diplomat -- he leaned on an old Senate colleague to help him out: Vice President Joe Biden.
After Mr. Kerry extracted an agreement from the Syrian opposition leader, Mouaz al-Khatib, to show up, Mr. Biden sealed the deal with a follow-up call. The vice president, who had met Mr. Khatib at a security conference in Munich, praised him for his courage, told him how important the meeting was and promised to stay in touch, according to the White House.
It was a classic example of how Mr. Biden has used personal relationships to amass influence in the Obama administration -- a talent that current and former officials predicted would allow him to further expand his influence on foreign policy during President Barack Obama's second term.
Mr. Biden will shift to another part of the Middle East today, when he will set the stage for Mr. Obama's first presidential trip to Israel later this month, in a speech to the annual conference of the American Israel Public Affairs Committee, an influential pro-Israel lobbying group.
When Mr. Biden last spoke to the group in 2009, he warned them "you're not going to like this," before laying out Mr. Obama's demand, largely rebuffed, that Israel stop building Jewish settlements in the West Bank. This time, officials said, he will be more conciliatory, presaging a less confrontational approach during the president's visit.
Mr. Biden, officials said, used his ties on Capitol Hill to champion another unpopular cause: Chuck Hagel, also an old Senate friend. With Mr. Hagel under attack over his positions on Iran and remarks he made about Israel, officials said Mr. Biden worked the phones to help eke out his confirmation as defense secretary.
Just as important to Mr. Biden's rise is his role in policy debates. With the exception of the raid on Osama bin Laden, which Mr. Biden famously advised delaying, there are few big policy deliberations in which he has not lined up with Mr. Obama. On issues like Afghanistan or Syria, his cautious instincts have prevailed over those advocating a more aggressive course.
In addition to pushing for a faster timetable for withdrawing troops from Afghanistan, he was also among those who opposed supplying weapons to the rebels in Syria -- a proposal developed by David H. Petraeus, the former director of the CIA, and supported by Hillary Rodham Clinton, then the secretary of state. Mr. Biden was joined in resisting the proposal by Thomas E. Donilon, the national security adviser, with whom he -- not surprisingly -- also has longstanding personal ties.
Besides being advocates of more aggressive policies, Mrs. Clinton and Mr. Petraeus, along with former Defense Secretary Robert M. Gates, each brought stature and independence that their successors cannot match, another contributor to Mr. Biden's increased role.
Mr. Obama gave Mr. Biden his own turf in the first term by handing him the Iraq portfolio, and the vice president helped engineer the brisk American withdrawal from that war. But with Iraq receding as an issue for the United States, the question is, what turf might Mr. Biden try to claim now?
China offers a tantalizing possibility, given that he has cultivated ties to its incoming leader, Xi Jinping. Mr. Biden spent hours with Mr. Xi, the Chinese vice president, during a trip to China in 2011 and again last year, when he played host on a visit to Washington.