Chuck Hagel may not wind up like John Tower.

But he could end up like Chuck Hagel.

For weeks, Republicans and Democrats alike have expressed skepticism about the former GOP Nebraska senator after President Obama tapped Hagel to succeed Leon Panetta as Defense Secretary. Once the murmuring started, students of history began invoking the ghost of the late Sen. John Tower (R-TX).

Tower holds a dubious spot in American politics. Since the inception of the republic, the United States Senate has rejected just nine nominees to a president's cabinet.

Tower is one of them.

And the Senate has only once rebuffed a former senator for a cabinet post.

That ignominious distinction belongs solely to Tower.

Chuck Hagel faces a rugged confirmation road ahead. His fate may not be as odious as Tower's. But the Senate could make a name for Hagel in an altogether different way.

The Senate has never formally filibustered a cabinet nominee. Senate rules require 60 votes to break a filibuster. Political handicappers believe Senate Democrats could successfully overcome such a procedural tactic to try to derail Hagel.

However, like the Tower nomination, it would be a first for the United States Senate.

"I would be disappointed and surprised if the Republicans were willing to filibuster one of their former colleagues for Secretary of Defense," said White House spokesman Jay Carney Friday.

But that doesn't mean it wouldn't happen. Opposition to Hagel is exceedingly strong in some quarters.

It's telling that after Hagel's confirmation hearing, not a single senator - Republican or Democrat - praised his sluggish performance. Only Senate Armed Services Committee Chairman Carl Levin (D-MI) extolled Hagel once he gaveled the seven-and-a-half-hour session to a close.

"I think he really advanced his own cause here today," lauded Levin.

Vote counters suspect Hagel will marshal a simple majority of 51 votes for confirmation. Still, a senator or a team of senators could set precedent by filibustering Hagel's nomination.

Multiple Senate sources believe that scenario is likely.

Here's the parliamentary problem for Hagel:

Most garden-variety bills create two opportunities to filibuster in the Senate. First, there's the "motion to proceed." That's the effort to actually summon a measure to the floor for discussion. The second chance to filibuster is at the end of debate on the actual bill. That's where senators could filibuster to prevent the package from coming to a final vote.

If there's a single objection or any other type of filibuster, the Senate must go through an exercise of "invoking cloture" to halt debate at each of those points. That requires garnering 60 votes on the motion to proceed to start the bill and again rounding up another trove of 60 to finish.

But unlike bills, many nominations - including those for Secretary of Defense - are what the Senate terms as "privileged." That means they go straight to the front of the parliamentary line, not having to navigate the initial filibuster trap of 60 votes on the motion to proceed. The only chance to block the nomination comes when debate is concluding. Senators could then erect a roadblock to prevent it from advancing to a final vote.

This helps Hagel some, but not much.

There are 12 Republican senators, including Senate Minority Whip John Cornyn (R-TX), who are now officially on record as opposing Hagel. That's not enough to torch Hagel's nomination as Democrats hold a 55-45 advantage in the Senate (two independent senators caucus with the Democrats). But a few Democratic defections could create trouble in clearing the 60 vote barrier if someone decides to filibuster.

It's important to note that even though a senator may oppose a nomination or a bill, some still vote for cloture (to end debate). The prevailing theory is that a president deserves to have an up-or-down vote on his cabinet nominee. However, it's another matter if the Senate confirms or dismisses the nominee under its Constitutional charge of providing advice and consent. That's why there has never been a true filibuster of a cabinet nominee.

It's improtant to note that the new filibuster rules do not apply when it comes to this sort of nomination.

"I can't imagine there will be at least one senator objecting to going to a final vote," said one Senate aide.

So getting to 51 votes for confirmation of Hagel is challenging to start with. Securing 60 votes to stave off a possible filibuster becomes dicey.

That's why the Tower confirmation ordeal bears study. Many thought that confirming a Defense Secretary would be a lay-up when President George H.W. Bush tapped Tower for the Defense Secretary post in 1989. First, the Senate had only rebuffed several cabinet nominees in 200 years. And, Tower was a former senator. Part of the club.

But Tower's nomination flamed out. No one filibustered Tower. But the Senate repudiated one of its own 53-47.

It's a new day in the Senate. For better or worse, it's no longer the clubby, chummy institution it used to be. Now it's stocked with tea party loyalists like Sens. Ted Cruz (R-TX), Ron Johnson (R-WI), Mike Lee (R-UT) and Rand Paul (R-KY). They don't do things like the "old" Senate. Tograsp this, all one must do is examine Thursday's vote on a bill to suspend the debt ceiling and require lawmakers to pass a budget or have their pay escrowed. Thirty-three Republicans, including Senate Minority Leader Mitch McConnell (R-KY) and Cornyn voted no - on a package crafted by House Republicans. Astute Senate observers wouldn't be surprised to discover a paradigm shift and witness a filibuster on Hagel's nomination.

Tower was the last cabinet nominee the Senate turned back. But the one prior to Tower came in 1959. President Dwight Eisenhower nominated Lewis Strauss to become Commerce Secretary. The Senate ultimately defeated Strauss's nomination, 49-46. Interestingly this unfolded just as Allen Drury's Pulitzer Prize-winning novel "Advise and Consent" hit the bookshelves. The novel (later converted into a 1962 film) focused on the efforts of a fictitious president to nominate a controversial figure for Secretary of State.

The Senate first defeated a cabinet nomination in 1834 when it voted against President Andrew Jackson's nomination of Roger Taney to become Treasury Secretary.

And if you were around in the 1840s, the last thing you wanted was to have President John Tyler nominate you for his cabinet. Tyler assumed the presidency after the untimely death of President William Henry Harrison, just a month into his term. That triggered legendary struggles between Tyler and Congress, including the first-ever impeachment attempt.

As a result of his tangles with the legislative branch, four of the nine cabinet nominations ever defeated by the Senate came during Tyler's watch. The Senate turned down Caleb Cushing for Treasury, David Henshaw for Navy (when that was a cabinet department), James Porter for War (which later become the Department of Defense) and James Green for Treasury.

The Cushing nomination was epic.

Tyler nominated Cushing three times and watched the Senate defeat him each time over a period of two days. And repeatedly renominating Cushing didn't exactly bolster his chances on the next round. Cushing netted19 yeas on the first vote (this was back when the Senate only had 48 members), ten on the second try and a paltry two on the third go around.

Not exactly "growing the vote."

Two other former senators have withdrawn their nominations before a final vote: Whig Thomas Ewing of Ohio and former Senate Majority/Minority Leader Tom Daschle (D-SD). President Andrew Johnson nominated Ewing for War Secretary in 1868. That nomination never made it out of committee. Four years ago, President Obama tapped Daschle to head the Department of Health and Human Services. Daschle later withdrew.

Filibusters for lower-level nominations are more common. The Senate voted against invoking cloture on President George W. Bush's nomination of John Bolton to become Ambassador to the United Nations in 2005. Bolton only secured 54 yeas when 60 were needed to advance to a final vote.

The Senate also filibustered the nomination of Richard Cordray to lead the Consumer Financial Protection Bureau in 2011. Cordray pocketed 53 yes's when 60 were needed. Mr. Obama controversially slid Cordray into his position via a "recess appointment 13 months ago. The Constitutionality of the president's scheme to install Cordray in that matter remains unsettled.

While the Senate has only torpedoed a fraction of cabinet-level nominations, senators have shunned about one-third of all Supreme Court nominees.

But the Senate has only filibustered one pick for the High Court.

In late 1968, President Lyndon Johnson nominated Associate Supreme Court Justice Abe Fortas to succeed Earl Warren as Chief Justice of the United States. In those days, it took 67 votes, not 60, to overcome a Senate filibuster. With the presidential election less than a month away, Johnson failed to conjure up the necessary votes to advance Fortas's nomination past cloture and to a final vote, requiring a simple majority.

So Hagel's path to the Pentagon is unclear. Hagel's chances for confirmation are enhanced now that Sens. Chuck Schumer (D-NY) and Barbara Boxer (D-CA) have announced their backing. But the Senate could enter a new era if senators decide to filibuster Hagel's nomination.

And if there's a filibuster, Hagel's name will go into the history books alongside Abe Fortas and John Tower - even if the Senate confirms him as President Obama's Defense Secretary.