Some may be familiar with American TV from the 1970-1980's. If you are, then you're familiar with the show called "Happy Days".
You may remember the episode when the Cunninghams (and Fonzie, and Ralph, and Potsie) were on holiday at the beach. Fonzie had a fear of water. Through a set of hard-to-believe circumstances, he is challenged to water-ski jump over a shark cage. Ever the man, he dons his leather jacket, hops on water skis, and jumps the shark to save his cool-ness.

Many connoisseurs of late 70s/early 80s TV pin this exact episode as the moment where the TV show "Happy Days" went from acceptable to bothersome. And thus the phrase "Jump the Shark" has meant similar things to me.
Here, today, it is my opinion that Bart Ehrman has "jumped the shark".
I just read his essay in the Gospel of Judas, pp. 77-120 over my lunch hour. (The essay isn't that long, the typography of the whole book is super-padded in an effort to get close to 200 pages). And while overall there is good, solid information in the essay, there are flashes where one can only say, "Why, Bart? Why?!". One of the most egregious is below.
We aren't sure when this gospel was written. The copy in our possession appears to date from the end of the third century—around 280 or so (250 years after Jesus' death). But that doesn't tell us when the book was originally composed. In the case of the Gospel of Mark, for example, we don't have any surviving copies until after the third century, but Mark, most likely the first of the canonical gospels to be written, was almost certainly composed by 65 or 70. The earlier copies have all been lost, worn out, destroyed. So too with the earlier copies of the Gospel of Judas. (Ehrman, p. 81)
Holy non-sequitur, Batman! One leaves the paragraph thinking that it's possible Judas was written at the same time Ehrman postulates for Mark—65 or 70. He leaves the comparison to Mark hanging, the last sentence of the paragraph seemingly implying (though not really) that Judas is similar. A careless reader could easily connect the lingering dots and think, "well ... if that happened with Mark, why not Judas?"
Ehrman's following paragraph mentions that a reference to Judas (a reference, not a citation) is found in Irenaeus, which dates to around 180. This brings us closer to the likely situation. But this is Ehrman's only allusion as to date of original composition of the Judas we have until 10 pages later, pp. 91: "... most will probably date [Judas] to 140-160 or so". And it is less than clear (particularly to the careless reader) leaving the Mark-Judas comparison dangling.
My other primary reason for thinking the shark has been jumped is with the insistent lumping of orthodox Christianity ("orthodox" in a doctrinal sense [e.g. in alignment with the Apostles Creed and other ecumenical creeds]) with gnostic spiritualities. I half get the sense that if I worship at the church of Dan Brown I can still consider myself Christian. It seems as if Dr. Ehrman has the opinion that if one's religious sensibilities have anything to do with Christ in any way, then that one can be called a Christian.
But Dr. Erhman's essay itself distinguishes the problem with referring to gnostics as Christian: in general, gnostics deny that Jesus was fully God and fully man. They'd cringe at the Symbol of Chalcedon. We embrace it. Also, gnostic spirituality, as Dr. Ehrman describes it (and I think he's right) focuses on seeking salvation (freedom from material world and transference into a completely spiritual being) for one's self and achieving it by one's self. Christianity is most definitely not about achieving salvation on one's own terms. It is about the worship and glorification of God who provides salvation for us in the person and work of His Son Jesus Christ.
Lumping this all together under a label of "Christian" is not helpful to the discussion. Adding in the concept of competing "Christianities" with winners and losers (Irenaeus == 'winner'; Gospel of Judas/Gnostics == 'loser') where the winners write history and therefore define proper doctrine is a distraction.
Again, to be fair, Ehrman doesn't come out and say this straight up. But it is alluded to throughout. Language of "winners" and "losers" (or inclusion and exclusion) in canonicity battles is frequent—but Gospel of Judas doesn't appear on any canon lists we know of, does it? So how could it have been "excluded"? This style of allusion happens, for instance, on p. 116:
The New Testament consists of twenty-seven books that the victorious orthodox party accepted as sacred texts conveying God's word to his people (Ehrman, 116).
And this sort of thing is just my problem with this particular essay. Most of the essay is excellent and fairly explanatory. But then stuff like the above slips in and makes one (well, me, anyway) cringe.
And that's why I think Bart Ehrman has "jumped the shark". Not that his scholarship is suspect per se; please don't think that. It is the forced and obvious leaning toward sensationalism that I'm starting to tire of. I consistently use his edition of the Apostolic Fathers and for the most part like the translation and find the notes helpful (though a little light on the textual criticism side of things). I wish he'd return his focus to those sorts of projects.
Please, Dr. Ehrman, now that you're over the shark cage, please return to editing new critical editions and translations of some early Greek texts and leave Time, Newsweek and 60 Minutes to others.