Former Sen. Chuck Hagel may survive the protracted and contentious confirmation process for the top job at the Pentagon, but his rocky road to confirmation will likely make him a far weaker defense secretary, say defense and foreign policy experts.

"I think Hagel will be on short leash in terms of what he can say and what he can do," said Loren Thompson, head of the Lexington Institute, an Arlington-based foreign policy think tank.

The Democrat-controlled Senate is scheduled to vote on Hagel's nomination as defense secretary as early as Tuesday after failing last week to secure the 60 votes he needed to win confirmation.

In a nearly unprecedented maneuver, Hagel's fellow Republicans filibustered his nomination, citing a poor performance during his confirmation hearing and what they see as a weak stance on defending Israel and stopping Iran from acquiring nuclear weapons.

Many Senate Republicans plan to oppose Hagel again next week. On Thursday, 15 GOP senators wrote to President Obama asking him to withdraw Hagel's nomination, a rare move that could further diminish Hagel's status if he takes the helm at the Pentagon.

The senators cited the widespread GOP opposition as reason enough to yank the Nebraska lawmaker's nomination, noting that no defense nominee over the past 50 years has been opposed by more than three senators.

The senators expressed concern about Hagel's lackadaisical performance at his Jan. 31 confirmation hearing, which they said raised "serious doubts about his basic competence to meet the substantial demands of the office." Hagel struggled in that hearing to show basic knowledge of defense matters, twice misstating the U.S. position on preventing Iran from obtaining a nuclear weapon.

GOP opposition is probably not enough to keep the former Nebraska lawmaker from winning confirmation, since several Republicans who helped block a vote on his nomination last week now say they won't block it a second time when Congress returns next week. The GOP senators say they will adhere to a long-standing tradition of not permanently filibustering presidential Cabinet nominees.

But if confirmed, Hagel may not get the same kind of respect and trust as a nominee who was approved by unanimous or widely bipartisan support, foreign policy experts say.

"It's a disaster," Danielle Pletka, a foreign policy and defense scholar at the American Enterprise Institute, told The Washington Examiner.

Pletka cited senators' complaints that Hagel failed to disclose all of his past speeches and other information they requested, which could raise questions about his trustworthiness.

"I can't see how he could be any weaker," Pletka said.

Thompson added that the opposition to Hagel domestically could limit "how much influence he has with foreign leaders."

The White House on Thursday defended Hagel, pointing to the handful of GOP senators who say they will now vote to confirm him, including Sens. Richard Shelby, R-Ala., and Thad Cochran, R-Miss.

Experts say Hagel could redeem himself in lawmakers' eyes once he is confirmed, but there will be no honeymoon period with Congress.

"The nicest thing you could say about Hagel is he is going to have to prove he has the competency to do the job," said James Carafano, a defense policy scholar at the conservative Heritage Foundation. "It's not an enviable position to be in."