As President Barack Obama's top candidate for defense secretary, Hagel has another credential important to the president: a personal relationship with Obama, forged when they both were in the Senate and strengthened during overseas trips they took together.
Hagel, 66, emerged last week as the front-runner for the Pentagon's top job, four years after leaving behind a Senate career in which he carved out a reputation as an independent thinker and blunt speaker.
Wounded during the Vietnam War, Hagel backed the Iraq war, but later became a fierce and credible critic of the Bush administration's war policies, making routine trips to Iraq and Afghanistan. He opposed President George W. Bush's plan to send an additional 30,000 troops into Iraq — a move that has been credited with stabilizing the chaotic country — as "the most dangerous foreign policy blunder in this country since Vietnam, if it's carried out."
While Hagel supported the Afghanistan war resolution, over time he has become more critical of the decade-plus conflict, with its complex nation-building effort.
Often seeing the Afghan war through the lens of his service in Vietnam, Hagel has declared that militaries are "built to fight and win wars, not bind together failing nations." In a radio interview this year, he spoke broadly of the need for greater diplomacy as the appropriate path in Afghanistan, noting that "the American people want out" of the war.
If nominated — an announcement could come this week — and confirmed by the Senate, Hagel would succeed Defense Secretary Leon Panetta. Panetta has made it clear he intends to leave early next year, but has not publicly discussed the timing of his departure. He took the Pentagon job in July 2011.
At the same time, Obama is considering one of Hagel's former Senate colleagues, Democrat John Kerry, for the job of secretary of state.
To political and defense insiders, Obama's preference for Hagel makes sense.
The former senator shares many of the same ideals of Obama's first Pentagon leader, Republican Robert Gates. When Obama became president in 2009, he asked Gates to remain as defense secretary, the only Cabinet holdover from the Bush administration. Both Hagel and Gates talk of the need for global answers to regional conflicts and an emphasis on so-called soft power, including economic and political aid, to bolster weak nations.
"A Hagel nomination signals an interest in, and a commitment to continuing a bipartisan approach to national security," said David Berteau, senior vice president at the Center for Strategic and International Studies.
He said that Hagel's two terms in the Senate, before he retired in 2009, spanned the latter years of the post-Cold War military drawdown and the post-Sept. 11, 2001 buildup. "From a budget point of view he has seen both ends of the spectrum and that gives him a good perspective to start from."
Hagel's possible selection has been met with initial praise from key members of the Senate, including the chairman of the Senate Armed Services Committee, Sen. Carl Levin, who said Hagel would be "terrific."
The choice could trigger opposition from some Jewish groups and may worry Democrats concerned about Israel-related issues. Hagel has criticized discussion of a military strike by either the U.S. or Israel against Iran. He also has backed efforts to bring Iran to the table for talks on future peace in Afghanistan.
"The appointment of Chuck Hagel would be a slap in the face for every American who is concerned about the safety of Israel," said Matt Brooks, executive director of the Republican Jewish Coalition.
Hagel often straddled party lines and had some high-profile dustups with his Republican colleagues.
In 2008, he criticized Republican vice presidential candidate Sarah Palin, saying she lacked foreign policy credentials and that it would be "a stretch" to consider her qualified to become president. His wife, LilibetHagel, endorsed Obama in his first run for president. Hagel also was mentioned as a possible candidate for Pentagon chief when Obama was first elected.
As defense secretary, Hagel would preside over the withdrawal of combat troops from Afghanistan and the waning days of the war, and would direct some of the steepest cuts in Pentagon spending in years. His task would be to restructure a pared down military that can step away from the grinding wars of the past 11 years and refocus on a swath of regional challenges from Syria, Iran and North Korea to terrorism in Africa and the defense buildup in the Pacific.
A big benefit will be his experience and his allies on Capitol Hill.
Defense analyst Loren Thompson, of the Virginia-based Lexington Institute think tank, said Hagel knows the political system and is known for thinking outside the box, which would help as budget cuts move forward.
"He's a veteran who understands how Congress works and has stayed plugged in to developments in defense policy," Thompson said. "He is not tied to the status quo and will think creatively about how to manage America's military forces."