[rhino369]

It's a fairly ubiquitous concept in DC. Hell, the website Zoe goes to work from in House of Cards is named after it.

[eli]

Hm, I'd assumed that was a reference to the newspaper/typesetting term "slugline". But maybe it's both.

[ghaff]

I'm not sure the "slugline" term is common for that meaning; it's typically (don't know how widely it's still used) just slug. But it's a pretty obvious and clever derived term to combine slug and headline and come up with slugline.

Slug line (two words) is apparently a screenwriting term--which I didn't know.

[eli]

I don't think slugline was derived from headline. On old linotype machines, the slug was literally a line of metal.

[rhino369]

That might be it actually.

[atwebb]

I'd assumed it was because they followed the trail left by politicians, but your explanation is less sticky so I'll go with that.