Growing unease about Chuck Hagel as Pentagon chief could lead Republicans to force the nomination to clear a 60-vote threshold on the Senate floor, lawmakers said Tuesday.

One of Hagel's most vocal opponents, Sen. Lindsey Graham, R-S.C., said he was sending a letter to the White House Tuesday, asking President Obama, “Did you make any phone calls to the Libyan government requesting their assistance” during the Benghazi attack.

“If he’ll answer that question, then I’m ready to move forward on Hagel,” Graham told National Journal. “My goal is not to block Hagel forever. My goal is to get a simple question answered,” Graham said.

“The White House has been very arrogant,” he added. “And this is one tool available to us in a minority party to get answers to basic questions.”

The Senate Armed Services Committee is expected to approve Hagel’s nomination as secretary of Defense on party lines in a vote scheduled for 2:30 p.m. Tuesday. But it remains unclear whether and for how long Republicans will drag out the vote on the Senate floor by requiring procedural hurdles like cloture, which would require a 60-vote threshold to proceed.

“We are going to see to it that he has a 60-vote threshold and by doing that, there are going to have to be 60 votes out of the United States Senate who want him to be secretary of Defense,” Sen. James Inhofe, R-Okla., the ranking member on the Senate Armed Services Committee, told Fox News on Tuesday.

It only takes one senator to demand the 60-vote hurdle be met and Inhofe said Tuesday that Republicans had a range of questions driving their desire to see that threshold to be met.

Most observers still expect Hagel to ultimately be confirmed but, if Republicans do insist on such a hurdle, it’s unclear where the votes would be. So far only two Republicans, Sens. Thad Cochran of Mississippi and Mike Johanns of Nebraska, have said they plan to support Hagel.

Sen. John McCain, R-Ariz., has not said which way he will vote on the floor.

Others, including Sen. Ted Cruz, R-Texas, still want more financial information from Hagel.

“I don’t know if I can stop it,” Inhofe said, but added he feels confident about his odds of defeating Hagel. “I give it a 55/45,” he said.

For his part, McCain walked back accounts that he was trying to convince Republican colleagues not to filibuster the Hagel nomination.

“I’ve stated my position,” McCain told a small group of reporters camped outside an Armed Services Committee hearing Tuesday on an unrelated issue. “But I don’t twist any arms.”

McCain has been critical of Hagel but reiterated his rationale for opposing the use of a filibuster, arguing it sets a bad precedent.

“Someday we’ll have a Republican president, we’ll have a Republican majority in the Senate. We don’t want to set dangerous precedents with filibusters. We are certainly free to express our views and vote but I don’t believe in filibusters of major cabinet appointments."

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