detecting and countering certain activities of foreign powers
Why did the foreign power flushed the toilet? Because it was its duty.
Anything can go under this one because by definition any European nation is a foreign power relative to US justice and vice versa. Similarly, flushing the toilet or putting another layer of lipstick on the pig can be classified as a "certain activity"
There is a GLARING ADJECTIVE OMISSION here. It is missing the adjective "HOSTILE". It needs at least one or two occurrences of it.
So in the absence of this adjective the shield allows for any USA (and vice versa) surveillance of pesky foreigners, just indirectly. That clause allows USA to continue surveillance on anything happening in Eu and vice versa and they can still exchange information as before. In fact, if anything, this agreement in this form and in the absence of this adjective sets in stone the status quo of the Bush and post-Bush era.