In English we have two /l/ sounds, commonly called the "light" or "clear" l and the "dark" l. They exist in complementary distribution, with the light l in onsets and the dark l in codas (and syllable nuclei, though in these cases the l is underlyingly in coda position). The clear l is a regular lateral approximant, with the tip of the tongue resting on the teeth or alveolar ridge, depending on pronunciation, and the dark l identical in apical (tip) placement, but with co-occurring velar constriction by the lamina (the blade of the tongue).
However, Tom Brokaw for some reason just doesn't like clear l's. Not only does he pronounce all his l's (including those in onset position) dark, he doesn't even articulate the apical feature of the sound, instead using only the back of his tongue for the velar articulation, resulting in what can sound at times like a French "r" or Arabic "gh".
On a side note, my understanding of the two different l's in English was an extremely important step in my pronunciation of Spanish, which only has clear l's. Try it yourself: say "lamp" and "awl". The former is a clear l, the only l in most languages. The second is a dark l.