The flood of “President Obama’s first 100 days” coverage in cable news saw many of the channels, especially CNN, obsessing over assigning letter grades to the new administration. After absorbing 14 weeks (and change) of cable’s reporting and ranting on the new Obama White House, I decided to assign some value-added grades of my own.

How are the cable channels doing? Not well — though I have an image in my mind of Fox News Channel CEO Roger Ailes’ eyes lighting up in the run-up to the Tea Party protests the same way that Faye Dunaway’s did in “Network.” Like Howard Beale (who was quoted often during those events), a ranting correspondent (in this case, CNBC’s Rick Santelli) rallied his constituency to give voice to their anger. The next step was obvious: How do we cash in? Or, as Dunaway’s character put it in “Network,” “I want angry shows.”

Broken down, here are not-even-mid-term grades on how the cable nets’ are performing (alphabetically by network), with helpful mnemonic acronyms to go with each basic letter grade:

CNN: D, as in D.W.E.E.B. (Dumb, With Egregiously Enervating Bluster). The more I watch them, the more I’m convinced CNN’s problems are largely of its own making. There is an opportunity for the network between the polarized space on Fox News and MSNBC. But CNN is so relentlessly disappointing — so thoroughly preoccupied with meaningless toys, like having viewers go online to assign their own statistically insignificant letter grades to the president — that it’s difficult to take refuge there.

Every day, CNN seems to provide “The Daily Show” fresh fodder that renders the network ripe for ridicule. Until the network curbs those excesses, it’s going to continue alienating natural allies in the media sphere that would otherwise like to embrace the notion of a down-the-middle news channel.

Fox News: C, as in C.A.R.P. (Crazily Angry, Righteously Purposeful). Unlike CNN, Fox knows exactly what it’s about, and what its goals are. With the Republican Party in disarray, Fox’s high-profile talent (along with Rush Limbaugh) has become the voice of the opposition. Indeed, more than ever Fox functions like a TV version of talkradio, a medium that relies on keeping a small, like-minded audience listening (or here, watching) longer to pump up its average rating.

The only problem now is that as FNC’s hosts become increasingly successful, they become harder to rein in and keep from spilling into a level of vitriol that will embarrass parent company News Corp. — unleashing a Don Imus moment, such as the one that recently got Boston radio personality Jay Severin suspended. Sean Hannity and Glenn Beck work best as voices for angry conservatives, but not when they cross the line into wing-nut territory. Similarly, Bill O’Reilly’s obsession with “smear merchants” that dare criticize him — devoting parts of his show to paranoid-sounding personal grievances — continues teetering on the verge of a meltdown, not exactly the kind of precarious perch a network would covet for its top-rated host.

MSNBC: B-, as in B.O.O.R. (Bright, Only Overly Rude). The addition of radio personality Ed Schultz — another progressive — has added volume but not intelligence to the channel’s lineup. As a consequence, MSNBC’s positive profile still hinges almost entirely on Keith Olbermann and Rachel Maddow, both smart when discussing policy matters with regular talking-head contributors like law professor Jonathan Turley, but prone to bouts of unrestrained snarkiness when going after the political opposition. (Alec Baldwin registered much the same point on Huffington Post, though the “Fight! Fight!” response to a liberal actor chiding liberal hosts prompted him to clarify those remarks.)

It’s worth noting, too, that the lion’s share of MSNBC’s daytime anchors are consistently groan-inducing and bring to mind the over-hyped banality of most local broadcast news. That makes the primetime beachhead the channel has established a lonely island amid a sea of typical news blather and distasteful true-crime documentaries.