Whether you admire or detest him, it's important not to underestimate his intelligence or to discount his ability to connect as a lecturer.
His success owes a lot to the eclipse of military (and indeed of much political) history in American academia. Victor Davis Hanson, one of the best-known professors of the subject, discusses here the challenges of the field and how he almost backed into it as classical history Ph.D. candidate.
As Tumulty notes, Gingrich recognized well before September 11 the lack of a coordinated anti-terrorist strategy. As the investment ads say, "past performance is no guarantee of future results," but Gingrich is not just an opportunist who has moved into a vacuum, or what Paul Krugman, paraphrasing Ezra Klein on Dick Armey, called "a stupid person's idea of what a smart person is like."
While he is not a real military historian, Gingrich has a skill widely underestimated in elite academia: a fluency in grasping and expounding new ideas and moving them on to others. I've attended military and national-security conferences and have found officers more curious about ideas outside their specialties than many academics are.
Ten years ago I saw Newt Gingrich in action at a National Science Foundation-sponsored conference on social implications of nanotechnology. His remarks are here. Gingrich is obviously not a scientist, but his keynote made a strong positive impression on the participants I spoke with, some of whom had been highly skeptical about his intelligence. Of course he couldn't miss by calling for expanded support of scientific education and research, but he was skilled in presenting a scenario of the transformative potential of nanotechnology, about which there is still extensive debate.
The most interesting person to talk to at a party is not necessarily the one best suited to run anything. Openness to new ideas can also lead to the embrace of bad but intriguing ones. When it comes to the Republican candidates, Fran Lebowitz's comment on communism and fascism might be paraphrased: Romney is too dull, and Gingrich is too exciting.