Washington (CNN) -- Whenever a conflict pops up around the world, he has become the go-to guy, either rolling up his sleeves in the Senate or flying from hot spot to hot spot.
John Kerry is, after all, the chairman of the Senate Foreign Relations Committee, holder of one of the most influential positions in Congress and one of the United States' ambassadors to the world.
But recent events have made the Massachusetts Democrat's position on the world stage bigger than ever. He has become something of a shadow secretary of state, political observers say, and a possible successor to Hillary Clinton should President Obama be re-elected in 2012.
Over the past few months, Kerry has tackled uprisings in Egypt, Syria, Bahrain, Yemen and Libya. Over the weekend, Kerry was in Afghanistan and Pakistan. The trip was planned before the U.S. raid that killed terror mastermind Osama bin Laden at his compound in Abbottabad but took on new importance in its wake.
Pakistanis accused the U.S. of violating their sovereignty by launching a unilateral military attack inside the country. But some in the U.S. question how bin Laden was able to hide in plain sight without help from the Pakistani government.
Kerry told Pakistani Prime Minister Yousuf Raza Gilani and other officials in Islamabad on Monday that the United States need not apologize to Pakistan for the raid but that it it was in both countries' best interest to mend the frayed relationship.
Kerry said his goal in visiting was to begin a process that would leave the U.S. and Pakistan in a position where "isolated episodes, no matter how profound, do not jeopardize the relationships between our countries."
In Kabul on Saturday, a statement Kerry made about shifting the responsibility for Afghanistan's security to Afghan forces illustrated his role in U.S. diplomacy: the stature of speaking for the U.S. government without the responsibility of speaking for the U.S. government.
"Some of the moneys spent here can be spent more effectively," he said. "That less could be spent in certain ways. And that the footprint of our presence itself can be altered to become more effective and to see Afghans actually stepping out front more and assuming greater responsibilities.
"We're at a critical moment where we may be able to transition into that at a greater speed. But of course that's a military judgment and a White House judgment and one that will be made over the course of the next months based on Gen. Petraeus' recommendations," he said of Gen. David Petraeus, chief of the U.S.-led international military force.
White House spokesman Jay Carney said that although Kerry's trip was "independent" of the White House, it had its blessing. And Kerry conferred with Clinton, National Security Adviser Tom Donilon and Marc Grossman, the special U.S. representative on Afghanistan and Pakistan, before his departure.
Kerry was one of the first to call for Egyptian President Hosni Mubarak to step down as protests against him grew within the country this year. In a January 31 New York Times opinion piece, Kerry wrote that Mubarak "must accept that the stability of his country hinges on his willingness to step aside gracefully to make way for a new political structure.''
Obama had been criticized by Republicans and others for not calling on Mubarak to resign early on.
But at one point during the Egypt crisis, the White House called Kerry before he went on the Sunday talk shows and asked him to counter a statement by Clinton and former U.S. Ambassador to Egypt Frank Wisner that suggested a cautious timeline for Mubarak to step down.
The Boston Globe's Joan Vennochi opined that Kerry is angling to become the next secretary of state should Obama win re-election. Clinton has said that she will not stay on.
"As Egypt battles over its future, Senator John Kerry is negotiating his own," Vennochi wrote. "The Bay State's senior senator is running an unofficial campaign to become the next secretary of state. For once, he looks artful, as well as ambitious."
But are the rumors true?
"Absolutely not," Kerry spokeswoman Jodi Seth said. "Sen. Kerry's doing exactly what he's done for 26 years as a United States senator. He's doing his job, not looking for a new job."
But it's not the end of story for many watchers in Washington who see Kerry's political star rising since his unsuccessful run for president.
The Washington Post's Jackson Diehl wrote in late March that over the past two years, Kerry has "emerged as the Obama administration's key interlocutor with Syrian President Bashar al-Assad. Now he is putting the dictator on notice that he has reached a make-or-break moment in his relationship with the United States."
Seth said that "seeing the situation on the ground and asking tough questions of foreign leaders face to face is an integral part of the job."
Kerry was one of the first members of Congress to call for a no-fly zone over Libya to protect rebels from being attacked by armed forces loyal to Moammar Gadhafi.
Last week, Kerry invited Libyan opposition leader Mahmoud Gibril to Washington for meetings with members of Obama's security team.
He was also one of the first to call for al-Assad to stop reported violent and bloody crackdown on protesters.
Kerry, who met al-Assad last year, said at the time that he was convinced the U.S. could have a different relationship with Syria than it has in the past.
The two nations have "a mutual interest in having a very frank exchange on any differences that may exist, but also on the many, many agreements that we have about the possibilities of peace in this region," he said in a statement.
But that was then. Now, Kerry wants answers from al-Assad, who has failed to quell his government's brutality towards its own citizens.
During a Foreign Relations Committee hearing March 31, Kerry said that al-Assad failed to use a speech a day earlier to "promise concrete reforms, including lifting the emergency law. ... It is essential that his government refrain from using violence against its own people."
And he's had a part in handling the U.S.'s delicate relationship with Afghanistan.
Kerry, who supported Obama's 2009 troop surge in that theater, has been saying since early this year that the U.S. should accelerate the transition for security to the Afghans.
"It's fundamentally unsustainable to continue spending $10 billion a month on a massive military operation with no end in sight," he said.
Kerry has played the role of interlocutor for the Obama administration in Afghanistan before.
With Congress threatening to hold up funds for Afghanistan because of charges of corruption in President Hamid Karzai's government, it was Kerry who was dispatched to deliver a set of benchmarks that the White House demanded Karzai meet and tamped down on anti-Karzai sentiment in Congress.
The CNN Wire contributed to this report.