When two donors to a rising fascist leader commit suicide, a conspiracy theorist FBI agent must investigate if there is a connection; but when he discovers an elaborate CIA plot to stop the fascist, he must put his country before the law, and protect future targets by killing their leader.

Is this in the US so FBI jurisdiction? Or foreign soil so CIA territory? I know sometimes FBI agents are sent abroad to investigate missing person cases (when a country requests help), complex bank fraud (like in Switzerland, Panama), but why here? That's my first question.

You wrote 'two donors', I don't know what donor means in this case. Perhaps you could elaborate on this. I would delete the 'must investigate if there is a connection', due to the reader already knowing that is what the FBI does. 'Stop the fascist', stop him from what? 'Future targets by killing their leader', leader of what, and who are these targets?

This seems to have too much information in it. It seems like you are also missing key components that would help you simplify AND have a stronger emotional connection.
I think you can get rid of the first part entirely.

Next you've got some confusion about who the villain/antagonist is. Is it the fascist leader? The CIA plotters?

Finally, where is the hook that will make this totally unique--something we've not seen before?