As U.S. President Barack Obama gears up finally to announce his nomination for the next secretary of defense, all signs point to Monday for the unveiling of Chuck Hagel, a former Republican senator from Nebraska.

Hagel, a decorated Vietnam War veteran who served two Senate terms (1997-2009) and has since acted as an intelligence adviser for Obama, has proven a controversial choice to replace Defense Secretary Leon Panetta. Though he is still a registered Republican and had a solidly conservative voting record on most issues, Hagel has become an outspoken dissenter from the more hawkish impulses of congressional neoconservatives.

In particular, Senate conservatives including John McCain, R-Ariz., have accused Hagel of being too soft on Iran and insufficiently committed to the alliance with Israel. Hagel has also spoken in favor of cutting back Pentagon spending, opposed the war in Iraq (after voting to authorize it), and endorsed Obama over McCain when the two were campaigning for the presidency in 2008.

Though Hagel enjoys the support of many Democrats, some liberals are troubled by an offensive comment he made in 1998. At the time, then-President Bill Clinton was touting James Hormel, a gay philanthropist and campaign backer, to be ambassador to Luxembourg.

Hagel opposed the nomination on the grounds that Hormel was “openly, aggressively gay,” adding that this might interfere with Hormel’s ability to perform his duties effectively. (Clinton eventually named Hormel by a recess appointment when Senate Republicans blocked a confirmation vote.)

Hagel has since apologized, and Hormel says he has accepted the apology, but his nomination as defense secretary has been criticized by gay groups and politicians including just-retired Rep. Barney Frank, D-Mass., who said in a statement that Hagel’s “aggressively bigoted” comment should not be pardoned.

“I cannot think of any other minority group in the U.S. today where such a negative statement and action made in 1998 would not be an obstacle to a major presidential appointment,” added Frank.

But despite the strong opposition from figures on both ends of the spectrum, Hagel has already been vetted and, according to anonymous officials’ statements as reported by Politico and Reuters, is almost certain to be formally nominated to replace Panetta on Monday.

And that will be the only the beginning of the confirmation process. Assuming the Monday nomination comes to pass, Hagel will then be questioned by the Senate Committee on Armed Services, which consists of 12 Republicans, led by ranking member McCain, and 14 Democrats, led by Committee Chairman Carl Levin, D-Mich.

Opponents of Hagel’s nomination have made plenty of noise about these committee hearings, insisting that Hagel be subjected to a tough line of questioning. Former Sen. Joe Lieberman of Connecticut, who just retired from the Senate, told CNN last month that “If I were in the Senate on the Armed Services Committee, if he was nominated, I would have some real questions to ask him.”

“I think this would be a very tough confirmation process. I don't know how it would end," he added.

Sen. Lindsay Graham, R-S.C., who will have a seat on the Armed Services Committee, echoed Lieberman’s thoughts.

“I don’t think [Hagel]’s going to get many Republican votes,” he told NBC’s “Meet the Press.”

But in truth, confirmations for Cabinet members are not typically fraught; Panetta was confirmed with 100 percent of the senatorial vote in 2011. Even though the nomination of Hagel is seen as much more controversial, only one member -- Sen. John Cornyn, R-Texas -- has said outright that he would vote no, according to the Wall Street Journal.

On confirmation voting day in the Senate, Hagel only needs to swing a majority, which should be an easy task since the 113th Senate consists of 45 Republicans, 53 Democrats, and two independents who caucus with Democrats.

Obama has heaped praise on Hagel ahead of the expected nomination. As he told NBC’s “Meet the Press” on Dec. 30, “I've served with Chuck Hagel. I know him. He is a patriot. He is somebody who has done extraordinary work both in the United States Senate, somebody who served this country with valor in Vietnam.”