When he stepped into his new office at the Pentagon, replacing Marine Gen. Peter Pace as the senior military adviser to the president and the defense secretary, Mullen already was on record expressing his war worries with an unusual degree of candor.
"I understand the frustration over the war. I share it," he told his Senate confirmation hearing July 31. It weighs heavily on the minds of people in the United States, he said, and "it weighs heavily on mine."
As evidence of his focus on Iraq, Mullen has told Congress he intends to travel to Baghdad immediately after he takes over so he can see firsthand how the war effort is going.
Yet his agenda also is about the future, he said during his swearing-in ceremony at Fort Myer, a U.S. Army post near the Pentagon. "The fighting in Iraq and Afghanistan will one day end," he said. "We must be ready for who and what comes after."
Mullen, 60, was Defense Secretary Robert Gates' choice to replace Pace, who had been vice chairman of the Joint Chiefs when the Iraq invasion was launched in 2003.
Senior officers blame Pace for not standing up to former Defense Secretary Donald Rumsfeld, reports CBS News national security correspondent David Martin. Troops he pledged to support are now forced to serve extended 15 month tours in Iraq.
In June, Gates announced that Pace would retire rather than serve a second term as chairman -- not because of his performance in the job but because of political heat over the war.
Pace had wanted to serve two terms as chairman but got only one - another casualty of war, adds Martin.
Adm. Gregory G. Johnson, who retired from the Navy in December 2004 and has known Mullen for 20 years, said he believes Mullen will find ways to ensure that his views on the war are heard clearly.
"He is a sophisticated Washington player," Johnson said in a telephone interview. "He knows how to operate in that environment, so I think he will be greatly advantaged" in the war councils.
Coming in as Gates' choice to provide military advice gives Mullen "an incredibly strong hand," Johnson said. "He will play it adroitly and in a very sophisticated manner," to the advantage of the military.
Mullen arrives at a critical point in the war.
After building up U.S. forces in the first half of this year, despite some misgivings by the Joint Chiefs, Mr. Bush now has committed to ending the increase by July. Yet it is unclear whether Mr. Bush is any closer to the buildup's ultimate goal of getting the Iraqi government to move toward a peaceful reconciliation.
If the picture is still murky in July, will Mr. Bush proceed with further troop cuts? That is the kind of decision in which Mullen's view might carry weight.
As the chief of naval operations for the past two years, Mullen had a lesser role in the conduct of the war, given that most of the fighting is done by soldiers and Marines. Even so, he has let it be known that he is troubled by the broader effects of an escalating military commitment in Iraq.
"I worry about the toll this pace of operations is taking on (the troops), our equipment and on our ability to respond to other crises and contingencies," Mullen told the Senate Armed Services Committee.
He has made it clear that he agrees with a central tenet of the current U.S. strategy in Iraq -- that establishing security is critical to giving the Iraqi government the "breathing space" it needs to find a power-sharing formula. But he also sees limits to how long the military can wait.
Political reconciliation and economic growth are equally important to stabilizing Iraq, he said. "Barring that, no amount of troops and no amount of time will make much of a difference," he told the committee.
Mullen also has emphasized his concern that strains from the long wars in Iraq and Afghanistan may detract from the country's ability to handle threats elsewhere.
"To the degree that we narrow our focus solely on those two pieces of the overall global puzzle, we lose sight of other state and non-state threats in the region and around the world," he said in remarks to a conference on national security last week. He mentioned North Korea as a missile threat.
Mullen's concerns about the impact of the prolonged war on troops and their families is in line with Gates' thinking. Together, they might be expected to push for a quicker drawdown of U.S. troops in the second half of next year than Gen. David Petraeus, the top commander in Iraq, would like.
Loren B. Thompson, who follows military issues for the Lexington Institute think tank, said that during Mullen's tenure at the Pentagon as a deputy chief of naval operations from 2001 to 2003, he was considered the top budget expert in the Navy.
Mullen then was promoted to four-star rank and assigned as the vice chief of naval operations, the No. 2 job in the Navy, before going to Naples, Italy, in October 2004 to serve for nine months as commander of U.S. naval forces in Europe.
A native of Los Angeles, Mullen graduated from the U.S. Naval Academy in 1968. He turns 61 on Thursday.
He will be the first admiral to serve as chairman of the Joint Chiefs since Adm. William J. Crowe, Jr., who held the job from 1985-89, and only the fourth since the post was created in 1949. The other two were Adm. Arthur W. Radford, 1953-57, and Adm. Thomas H. Moorer, 1970-74.