> Some European agencies want the US government to spy on European citizens because it is illegal for them to do it themselves but it's not illegal for them to obtain information about European citizens from US spies.

Bingo, data sharing agreements between intelligence services.

NSA can't spy on US citizens but GCHQ can, and GCHQ can't spy ok UK citizens but NSA can.

Then just come up with a sharing agreement, and you're "golden".

It's all ridiculous.