If former Nebraska Sen. Chuck Hagel is nominated to be the next secretary of defense, it is unlikely that he will have a smooth ride to confirmation.

Leading the Pentagon would mean overcoming an already vocal opposition from pro-Israel groups and others who object to his stance on Iran and Hamas. One group began running ads on Washington-area television stations on Thursday, even though the Obama administration has not offered his name for consideration.

Should he be nominated to replace Leon Panetta, he would bring to the Pentagon a distinct bias against armed conflict forged during the Vietnam War.

Badly burned after his armored personnel carrier hit a land mine in Vietnam, Hagel sat in a medical evacuation helicopter thinking of the horrors he had experienced during his time in combat.

"If I ever get out, if I ever can influence anything, I will do all I can to prevent war," Hagel would later tell his biographer, Charlyne Berens.

The moment was seminal for the young soldier who volunteered to join the Army and ended up serving a yearlong tour in 1968 during the Tet Offensive, considered the most violent period in that war.

Hagel served side by side with his younger brother because of a clerical error. He earned two Purple Hearts, one of which was for saving his brother's life. The second Purple Heart was for shrapnel he took in the chest while on patrol with his brother by his side; his brother saved his life by patching up his wound.

Hagel's time in Vietnam forged his thoughts about combat for the rest of his life, earning him a reputation on Capitol Hill as a senator with an independent streak that meant he was sometimes at odds with his Republican colleagues.

"Not that I'm a pacifist -- I'm a hard-edged realist, I understand the world as it is -- but war is a terrible thing. There's no glory, only suffering," he is quoted as saying in his 2006 biography, "Moving Forward."

Hagel used his Vietnam experience when he criticized the Iraq war early on, including the surge, the plan to put more troops into that country, calling it, "the most dangerous foreign policy blunder in this country since Vietnam, if it's carried out."

Those decisions did not sit well with his Republican colleagues on Capitol Hill, and it hurt his chances to move up the ranks to power positions.

While serving in the Senate, Hagel became close with then-Sen. Barack Obama, and they seemed to find common ground about the use of military force and Hagel's fairly moderate approach to foreign relations issues. Obama also appreciated Hagel's willingness to buck his own party.

Hagel, Obama and Sen. Jack Reed also toured parts of the Middle East, including Iraq, in 2008.

"It was an extraordinary trip," Reed, a Rhode Island Democrat, told Security Clearance. "There was just an exchange of ideas about the region, and I think the president was also impressed with not only (Hagel's) understanding but the questions he raised, not just with the president but with the foreign leaders that we met," Reed said of the conversation between Hagel and Obama.

Hagel and Obama also have common ground when it comes to Iran. Both believe in open dialogue with Iran, though Hagel has argued against sanctions for the country, while the president has tightened the screws on Iran with tougher sanctions.

"By refusing to engage Iran, we are perpetuating dangerous geo-political unpredictabilities," Hagel said in a 2007 speech. "Our refusal to recognize Iran's influence does not decrease its influence, but rather increases it. Engagement creates dialogue and opportunities to identify common interests, demonstrate America's strengths, as well as make clear disagreements," he said.

In September, Hagel co-authored an opinion piece in the Washington Post backing the idea of "keeping all options on the table" for stopping Iran's nuclear program.

"Since the consequences of a military attack are so significant for U.S. interests, we seek to ensure that the spectrum of objectives, as well as potential consequences, is understood," it read. The piece did not rule out the possibility of using military force.

"That's not going to be his view as far as dealing with them in this position as secretary of defense. The president will tell him, direct him what the policy is," said William Cohen, a former Republican defense secretary who served under President Bill Clinton.

Hagel has also opposed efforts to isolate militant groups such as Hamas, a stance that has inflamed many, including pro-Israeli organizations.