The Senate is expected this week to confirm Chuck Hagel to be the next Pentagon chief, but the weekslong partisan battle over the former Republican senator from Nebraska has provided a taste of some of the biggest national security fights that lie ahead.

After a cloture vote on the controversial nominee narrowly failed earlier this month, the White House now appears to have the 60 votes necessary to defeat a filibuster and proceed to an up-or-down vote on Hagel as early as Tuesday.

The chamber will likely reconsider the failed cloture vote on Hagel at noon Tuesday. If it succeeds, the vote on confirmation would be either Tuesday or Wednesday, depending on whether there is unanimous consent to yield back post-cloture debate time.

Several Republicans, including John McCain of Arizona and Susan Collins of Maine, are expected to support cloture despite their opposition to the nominee. McCain voted against the first cloture motion on Hagel to allow more time for Republicans to get answers to outstanding questions.

“I do believe that elections have consequences, unfortunately, and the president of the United States was re-elected,” McCain said Sunday on CNN.

“I believe that when the questions are answered, and I believe they will be by this coming week, that the president deserves an up-or-down vote.”

For the vote on the confirmation itself, Hagel appears to have the backing of the 55 members of the Democratic caucus and at least three Republicans, giving him more than enough support for a simple majority once cloture is invoked.

Unresolved Policy Issues

But while Hagel taking over the helm of the Pentagon is all but a certainty, the issues that dogged his unusually arduous confirmation process — namely, Iran, Israel and nuclear weapons — are far from resolved.

During his Jan. 31 confirmation hearing, Hagel apologized for previous remarks on Israel and expressed support for a policy of prevention, rather than containment, on Iran and, if necessary, unilateral sanctions on Tehran. Despite a lackluster performance before the Senate Armed Services Committee, his comments during the hearing and in a series of one-on-one meetings with key lawmakers provided enough assurance to concerned Democrats that his views on those issues are in line with the White House’s and their own.

But Hagel will have a hard time shrugging off criticisms from the right that he has previously been too soft on Iran and too hard on Israel as he takes a post that has become increasingly focused on international affairs and coalition building in recent years. That shift in the top Pentagon job is only expected to continue under Hagel, a Vietnam veteran who was considered a foreign policy expert during his two terms in the Senate.

In a Feb. 21 letter, 15 Senate Republicans urged President Barack Obama to withdraw Hagel’s nomination because he did not have strong bipartisan support. The letter amounted to a last stand for GOP senators who had led the opposition to the nominee, but it also provided a preview of the political hurdles ahead for Hagel as he prepares to take over the Pentagon.

With Hagel as Defense secretary, the senators wrote that the military option on Iran would have “zero credibility.”

“This sends a dangerous message to the regime in Tehran, as it seeks to obtain the means necessary to harm both the United States and Israel,” they warned.

Concern Over Nuclear Arsenal

Hagel’s track record on nuclear weapons — particularly a report he co-authored last year calling for decreasing the size of the U.S. nuclear arsenal and eventually shedding the ground leg of the famed triad — will also continue to draw scrutiny from Republicans, particularly following Obama’s State of the Union promise to open talks with Moscow on further arms reductions.

Throughout his confirmation process, Hagel has assured lawmakers that he supports maintaining and modernizing the nation’s nuclear arsenal and opposes unilateral reductions to the U.S. nuclear inventory.

But many Republicans remain skeptical and will closely track decisions Hagel would soon make as Defense secretary on funding for expensive modernization programs such as the Air Force’s next-generation nuclear-capable bomber and the Navy’s replacement for its venerable fleet of Ohio-class ballistic missile submarines.

In a twist of timing, Hagel would take the top Pentagon job just as the military begins making significant investments in modernizing those multibillion-dollar programs. Their annual investments will only grow during the next decade, making them potential targets as the Pentagon faces the threat of the sequester or other deep cuts that could be part of a deficit reduction agreement.

Frank Oliveri contributed to this report.