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 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 .