The Sustainability of a Purely Evangelical Identity

Yesterday I got coffee with a friend and our conversation eventually turned to the topic of modern American evangelical identity. My friend voiced frustrations with the arbitrary nature of evangelicalism's identity with church history. For the most part, evangelicals do not stand in the tradition of which they are a member, so much as they label themselves with one tradition but borrow randomly from any other tradition they personally find useful.

While such an approach to church history is certainly American (and quite post-modern, in the most technical sense of the overused phrase) I wonder if it's healthy. My friend's contention is that evangelicalism can work when it's an ethos within a larger tradition. So, for example, you can have a working evangelicalism grounded in the Anglican tradition (C.S. Lewis, the Clapham evangelicals of the late 18th century, maybe Tom Wright?) or in the Reformed tradition (Schaeffer, Guiness, Keller) but you cannot have a a stable, lasting Christian tradition that is primarily evangelical because of evangelicalism's approach to church history.

I'm not sure if I agree with his argument or not, but I'm curious to hear what the readers of Mere O think. If there's a readership anywhere likely to think (and capable of proving) that evangelicalism can function on its own as a distinct and sustainable Christian tradition, I'm guessing this is it. So what say you?