As Chuck Hagel, the former Nebraska senator and now President Obama's nominee for secretary of defense, gears up for his confirmation process in the Senate, there is at least a possibility that he won't be cleared by the upper chamber to head up the Pentagon.

Just how often does the Senate oppose a Cabinet nominee to the point that he or she is rejected or withdraws? And for what reasons? Thanks to a research paper from James D. King, who heads the political science department at the University of Wyoming, we have the answers to these questions.

We encourage you to read the entire report, from which we've plucked out some charts illustrating three truths about the Cabinet confirmation process  -- two of which The Fix's Aaron Blake also noted in a recent post -- that reveal both good and bad news for Hagel's odds:

1) The vast majority of individuals whom presidents nominate to their Cabinets are confirmed by the Senate.

2) The defense secretary post has tended to be a source of very little controversy.

3) Public policy issues account for much of the opposition in the confirmation process.

Let's take a look at each point.

1. When presidents nominate individuals to serve in the Cabinet, they are almost always confirmed, which is good news for Hagel. Just 21 Cabinet nominees in history have been defeated or have withdrawn. And as the following chart from King's paper shows, just nine failed to survive the process between 1969 and 2008. Eight of them were withdrawn as nominees, and one (John Tower in 1989) was rejected in a vote.

(The chart only runs through 2008, so it's worth noting that in 2009, Obama's nomination of former Senate majority leader Tom Daschle to be secretary of health and human services was withdrawn.)

2. Compared to other departments, Defense nominees haven't tended to run into as much opposition. As the following chart shows, more than 9 in 10 have been confirmed with little or no challenge. Nominees to the Justice and Interior departments, by comparison, have faced more pushback, while nominees to head the CIA, Homeland Security Department, and Veterans Affairs have suffered more rejection.

Now, this doesn't mean Hagel won't run into opposition -- in fact, he already has. And it's worth noting that the rate of rejected/withdrawal of DoD nominees is higher than most other agencies. But it's also worth noting that history has shown a relatively good success rate for those who have tried to get confirmed as secretary of defense, after all is said and done. Of the 10 failed nominees since 1969, only one was nominated for defense secretary.

3. While Hagel may find some comfort in the above data, the next chart isn't as favorable. "Public policy concerns were expressed by senators in 70 percent of nominations encountering significant opposition and were the primary reason expressed in 57 percent of cases," writes King.

Much of the GOP opposition to Hagel lies in the policy positions he's adopted on Iran, Iraq, Israel and social issues, among other things. Hagel's opponents will have no shortage of material.