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Countering the Republican-led opposition to President Barack Obama's nominee for defense secretary is a less flashy but powerful constituency: military veterans.

Veterans' organizations have praised Chuck Hagel, a twice-wounded combat veteran of Vietnam and deputy administrator in President Ronald Reagan's Veterans Administration.

The Veterans of Foreign Wars has called him uniquely qualified to become Pentagon chief. The Military Officers Association of America said his experience gives him "a range of perspectives." The American Legion said he was a longtime advocate for veterans.

The organizations, which as congressionally chartered, stopped short of an outright endorsement.

Republican-leaning outside groups have waged a well-funded campaign against Hagel, airing television commercials, running full-page newspaper ads and expressing their opposition on local radio stations.

Officials from Americans for a Strong Defense, hoping to pressure Democratic Sen. Mark Pryor, spoke out on an Arkansas station this week.

Hagel's first test could come as early as Thursday with a possible vote in the Senate Armed Services Committee.

The committee chairman, Sen. Carl Levin, D-Mich., has said he would like to vote when the committee holds a hearing with Defense Secretary Leon Panetta on last September's deadly attack on the U.S. diplomatic facility in Benghazi, Libya.

Some Republicans on the committee are circulating a letter calling for a delay in the vote until Hagel provides more information about recent speeches, the groups he has addressed and their ties. Sen. Ted Cruz, R-Texas, is dissatisfied with what Hagel, a former two-term GOP senator from Nebraska, has disclosed so far.

"I'm not going to make any decision on Sen. Hagel until we get all the information we've requested," Sen. Lindsey Graham, R-S.C., told a small group of reporters on Wednesday. "I don't think we should be voting."

Democrats were working to resolve the last-minute issues.

Sen. John McCain, R-Ariz., said his staff was trying to determine whether Cruz's questions are "are keeping with the normal parameters of what nominees are supposed to provide or whether it exceeds that."

In a letter to Sen. Roger Wicker, R-Miss., who opposes the nominee, Hagel said he had been "forthright in disclosing all required information about my personal interests and holdings," but pointed out that the senator's request for financial information about private corporate and nonprofit entities "is, by contrast, not mine to provide."

Hagel said the information is "legally controlled by the individual entities and not mine to disclose."

Democrats hold a 14-12 edge on the committee and could hold a vote despite GOP objections.

The Associated Press obtained a copy of the letter.

The competing pressures on lawmakers from GOP-leaning outside groups and veterans' organizations — plus Hagel's military service — explain why many Republicans have announced their opposition to Obama's choice but have shown no inclination to filibuster the nominee, say congressional aides.

All 55 Democrats are expected to back Hagel, and Republican Sens. Thad Cochran of Mississippi and Mike Johanns of Nebraska have announced they will vote for him. Several Republicans, including McCain, have said they would oppose a filibuster.

Hagel's past votes and statements unleashed a barrage of criticism that he is too weak in his support of Israel, too tolerant of Iran and willing to slash the nation's nuclear arsenal. His halting performance at his confirmation hearing led Graham to urge the Obama administration to reconsider the nomination.

There are about 22 million veterans nationwide, and they hold considerable sway with Congress. While veterans are hardly in lockstep when it comes to a Democratic president's Cabinet choice, Hagel's personal story resonates with those who have served, says former Sen. Max Cleland, D-Ga., a triple amputee from the Vietnam War.

"He grew up in the heartland of America, goes to war, war of his generation," Cleland said in an interview. "He volunteers to walk point ... because he wants to do it on behalf of his comrades. He gets wounded twice. He still carries some of that shrapnel in his chest, and vows the second time he's wounded that if he's ever in a position to help out the grunts, the average serviceman, the combat soldier that he had served with, he will."

VoteVets, a left-leaning veterans group, has campaigned for Hagel through social media, old-fashioned letters to editors and 18,000 emails from some 9,000 people to all the members of the Senate.

Veterans are a significant part of the population in the home states of Republican senators.

McCain's home state of Arizona has 531,910 veterans, including 176,245 who served in Vietnam, according to figures compiled by the Department of Veterans Affairs.

Graham's South Carolina has 421,525 veterans, including 142,290 Vietnam vets. In Georgia, home GOP to Sen. Saxby Chambliss, there are 776,205 veterans, including 254,015 who served in Vietnam.

Texas has 1,675,689 veterans, including 560,927 from the Vietnam War. The state's two Republican senators — John Cornyn and Cruz, the newest member of the Armed Services Committee — announced their opposition to Hagel's nomination last month.

Hagel "passed the GI bill, he was right about Iraq, he was right about Afghanistan," said Jon Soltz, who served two Army tours in Iraq and is the chairman of VoteVets. "When you look at veterans' issues and these types of things, he's been excellent to us and he's one of us. He's been there. Ted Cruz hasn't been there."

Americans for a Strong Defense, one of the outside groups, continues to focus its campaign on states with undecided senators, such as Alaska, Louisiana and Arkansas.

"We found that our grassroots efforts have intensified since Chuck Hagel's disastrous confirmation hearing," said spokesman Ryan Williams. "People are more concerned now about his nomination given the lackluster performance he delivered in front of the Senate Armed Services Committee last week."

Williams, who recently worked for Republican presidential candidate Mitt Romney, said the group has reached out to local leaders to pressure senators while the organization churns out a steady stream of news releases critical of the nominee.

Danny Gonzalez of the group Move America Forward, a pro-military organization, said his group's approach is to "fire up the grassroots and get those people motivated. We're definitely going to notify our list about which senators have publicly stated they are thinking about supporting him, calling their offices, faxes, email."