In the latest Marist poll, Hillary Clinton is riding high, beating all possible Republican presidential candidates by at least eight points and most by double digits. Meanwhile, New Jersey Gov. Chris Christie's (R) reputation has taken a big hit. His favorable rating is 13 points lower than his unfavorable rating. And Americans have shifted over the past month from believing Christie is "mostly telling the truth" about the infamous bridge lane closures, to now believing Christie is "mostly not telling the truth."

The change is all the more notable given the fact that Christie held a slight lead over Clinton in a few December trial heats; Marist now shows the former secretary of State with a 21-point lead over the governor.

We all know why Christie has been sinking: lingering suspicions over his role in Bridgegate, much of which has been fueled by MSNBC's relentless coverage. A month ago, much of the pundit class was praising Christie's epic press conference for supposedly putting those suspicions to rest. Then MSNBC, led by former New Jersey political reporter Steve Kornacki, sought to highlight the many legitimate questions that have not been answered, overwhelming Christie's attempt to skirt media scrutiny.

But why hasn't Clinton suffered similarly in the past several weeks? Fox News has been just as tough on her regarding the Benghazi attack. Fox has the bigger audience. And Fox is the experienced TV muckraker, having gamely tried to tag the Obama administration with a series of supposed scandals such as Solyndra, Operation Fast and Furious, and the IRS auditing episode, often prioritizing such stories when more traditional outlets put them on the back burner.

Indeed, it is MSNBC's coverage that is packing the bigger punch and influencing the most voters. What is Fox doing wrong and MSNBC doing right? It comes down to credibility.

Fox's credibility is shot precisely because of its past experiences going down rabbit holes in hopes of tarring Democrats, breathlessly deeming multiple pseudo-scandals as "Worse Than Watergate."

While it's typical for media outlets to get hysterical and speculative in the heady early days of a potential scandal, more reputable ones change their tone once exculpatory evidence comes to light. Fox, however, tends to treat any reporting counter to its pre-cooked narratives as target for attack. For example, when the New York Times published a major investigative report debunking conservative-driven myths about Benghazi, Fox News aired segments such as "New York Times doing PR work for Hillary?" and "New York Times Benghazi Report Seriously Flawed."

On the other hand, MSNBC is exercising quality control. The network's reporters haven't been in the business of ginning up scandals regardless of evidence. They went all-in on Christie because they sensed a good story, and kept at it when their instincts paid off. Led by Kornacki's deep knowledge of the Jersey political world, MSNBC has been able to generate its own scoops and offer thoughtful, reported speculation that points journalists in new directions.

Of course, Fox sometimes hits upon a Democratic scandal that is not fictional, such as the 2011 sexting escapades of former Rep. Anthony Weiner. But MSNBC did not shy away from that either. After initially giving him the benefit of the doubt, Rachel Maddow put direct and tough questions to the congressman and Ed Schultz called for his resignation. Later, during Weiner's ill-fated 2013 mayoral run, Lawrence O'Donnell famously humiliated him to his face. MSNBC showed its willingness to be moved by evidence and hold Democrats accountable as well as Republicans, bolstering its credibility in ways Fox rarely does.

As a result, Fox has created itself a sizeable audience, but drowns it in a swamp of fever dreams and cuts it off from the reality-based community. MSNBC's audience may be smaller, but it's more influential and helps carry MSNBC's coverage farther.

The Christie administration may want to trivialize MSNBC as a "partisan network." Conservatives may scoff and call the network "obsessive." But MSNBC is drawing blood in a way that Fox's vaunted "Noise Machine" has been struggling to do in the Obama era.