Phil Levy of AEI tries to define modern protectionism:
To better recognize protectionism in its modern guises, we offer three broad categories of protectionist measures: Intentional protectionism encompasses measures that are explicitly intended to favor domestic industry over imports. Incidental protectionism occurs when measures can be readily justified on other grounds but also have the effect of obstructing import competition. Instrumental protectionism describes a burgeoning set of policies in which trade actions are used as a lever to change another country's policies.
He then explains each category in detail.
I think this is a great article. I may not agree with all of the specific points, but in my view the definition of protectionism is an important issue that is often overlooked. The term gets thrown around a lot, and I'm not sure people are always using it the same way. Most people would probably agree that fighting protectionism is a core purpose of trade agreements. But what exactly is the protectionism that we are fighting?
And then there's the question of what the full scope of trade agreements should be. In addition to protectionism, what else should be included? I'll leave that one for another day.