LL - Is the Court saying this wasn't a retaliatory arrest because there was probable cause or that it was retaliatory but supported by probable cause? I'm confused.
It's a confusing opinion.
The dispositive issue is immunity. A federal official has immunity, even for an unconstitutional action, unless prior law clearly established that the action was unconstitutional.
Here, no prior case had ever held an arrest with probable cause to be unconstitutional. So the holding was that the agent had immunity because he had probable cause to arrest, whether or not the arrest was retaliatory, so the court doesn't actually decide if it was retaliatory or not.