President Barack Obama and his choice for Defense Secretary, former Nebraska Sen. Chuck Hagel, left, laugh as current Defense Secretary Leon Panetta speaks in the East Room of the White House in Washington, Monday, Jan. 7, 2013, where the president announced his nomination of Hagel. WASHINGTON (AP) - In the middle of a bitter fight over a Republican president's nominee for defense secretary, a former White House occupant pleaded with senators to give the president his choice for the Pentagon job. "Unless there is conclusive evidence against the nominee, the Senate should respect the right of a new president to choose the men and women he believes are best qualified to serve in his Cabinet," former President Richard Nixon said in March 1989. Nixon's request fell upon deaf ears. The Democratic-controlled Senate, on a largely party-line vote, defeated the nomination of John Tower amid allegations that he was an excessive drinker, womanizer and held close ties to defense contractors - all charges that he denied. It was an ignominious outcome for the former four-term Texas senator as it marked the first time the Senate had rejected one of its own for a Cabinet post. Republican President George H.W. Bush, on the job barely two months, absorbed the political blow. More than two decades later, President Barack Obama's nominee for defense secretary, two-term former GOP Sen. Chuck Hagel, faces stiff opposition from fellow Republicans who are willing to ignore Nixon's plea - and perhaps even toss aside their own words from 24 years ago - and vote against Hagel. The two politically charged confirmation fights offer obvious parallels and notable differences, especially in a Senate short on traditional comity. In both cases, Democrats hold a 55-45 advantage in the Senate - good news for Hagel as his nomination gained some Democratic momentum this week with the backing of Sens. Chuck Schumer and Barbara Boxer. The two had expressed misgivings about whether he was sufficiently pro-Israel and anti-Iran. Senate Majority Leader Harry Reid, D-Nev., and Armed Services Chairman Carl Levin, D-Mich., already were in Hagel's corner, lauding the decorated Vietnam War veteran who would be the first enlisted man to head the Pentagon. Hagel met with Levin on Thursday in advance of his confirmation hearing on Jan. 31. Tower was up against near unanimous Democratic opposition led by the chairman of the Senate Armed Services Committee, Georgia's Sam Nunn, who argued that the nominee's behavior was a disqualification. Tower's history of alcohol abuse would prevent him from receiving a clearance "to command a missile wing, a (Strategic Air Command) bomber squadron or a Trident missile submarine," Nunn said. One of Tower's fiercest defenders was Republican Sen. John McCain, who had met Tower when he was a Navy liaison officer to the Senate and considered the Texan his mentor. In the drawn-out fight over Tower's nomination, McCain railed against what he considered the unfair treatment of the nominee, who had served as chairman of the Armed Services Committee. "I think it is of the utmost importance that we establish a clear record of what is being done to a good and decent man by this incredible process of allegations, and indeed, what is being done in the way of standards to be set for future nominees and to the traditional relationship between the executive and legislative branches," McCain said during the Senate debate in March 1989. In the next few weeks, all will be watching McCain, who once was close to Hagel but split with his fellow Vietnam veteran over the Iraq war and the 2008 presidential race. Hagel did not endorse in that race, a snub for McCain, the GOP presidential nominee. Hagel's wife, Lilibet, backed Obama. McCain has praised Hagel's service but stressed that he has serious concerns with some of his statements. The two have spoken on the phone since Obama announced on Jan. 7 that he had picked Hagel to replace Defense Secretary Leon Panetta. Hagel faces a robust outside campaign against his nomination and the announced opposition from six Republican senators, including the new ranking member on Armed Services, Sen. Jim Inhofe of Oklahoma. "We are simply too philosophically opposed on the issues for me to support his nomination," Inhofe said this week after meeting with Hagel. The conservative American Future Fund, which spent money to boost Republican Mitt Romney's presidential bid, launched its "Hagel No" campaign this week with ads as it looks ahead to Hagel's confirmation hearing. Several of the Republican senators opposed to Hagel - some stated their opposition before he was nominated or had a chance to meet him - are members of the Armed Services panel. Hagel faces the real possibility that he could emerge from the committee vote with not a single GOP senator backing him, a troubling development heading into the full Senate vote. Democrats hold a 14-12 edge on the panel, but Republicans Roger Wicker of Mississippi, Ted Cruz of Texas, David Vitter of Louisiana and Inhofe have said they will oppose Hagel. Other GOP senators have sent signals that they likely would vote against Hagel, with South Carolina Sen. Lindsey Graham calling Obama's choice an "in-your-face" nomination and New Hampshire Sen. Kelly Ayotte saying she was perplexed by the selection. Hagel can't even count on his home state senator, Nebraska's Deb Fischer. In last year's election, Hagel endorsed Fischer's Democratic rival, fellow Vietnam veteran and former Sen. Bob Kerrey. One of the few Democratic votes Tower got in 1989 came from Texas Sen. Lloyd Bentsen, who just months earlier was the vice presidential nominee on the Democratic ticket that lost to Bush and running mate Dan Quayle. Hagel may be a Republican, but he gets no extra points from his fellow GOP lawmakers. Seventeen current members of the Senate voted on the Tower nomination; so did Vice President Joe Biden, who stood with Democrats in opposing the nomination. In the rancorous debate, Republicans bemoaned what had become of the Senate process. "I find it fascinating to note the evolution of the standard by which we judge our fellow men and women," said Sen. Orrin Hatch, R-Utah. Jesus of Nazareth cautioned us to let him who is without sin cast the first stone. Next came the judicial cornerstone that a person is innocent until proven guilty. Now, however, we seem to say, if it is a presidential nominee, get him before we substantiate the facts. Republicans failed to sway the Democrats. The Senate rejected the nominee on a 53-47 vote. A year later, Tower settled some scores in his book, "Consequences: A Personal and Political Memoir," calling one Senate foe a "genuine boozer," another a "bully." He was promoting the book on April 5, 1991, when he died in a plane crash in Brunswick, Ga. EDITOR'S NOTE - Donna Cassata covered the Tower nomination fight for The Associated Press. Follow her on Twitter at http://www.twitter.com/DonnaCassataAP .