1. I think contracting should be easier than employing wrt bureaucracy and other regulations (e.g. no visas and the likes).
2. Timezone might be an issue?
3. What about rates? I guess US companies would prefer US contractors when they have the same rate as EU contractors?
Contracting with US companies from the EU will be easier or harder depending on the number of relationships you have with potential clients and the strength of those relationships.
It will also depend on specific market conditions of course.
And the overall economic climate.
Good luck.