The FBI infiltrated the Trump Campaign for President with one email. It was called the "Kremlin Connection". It was sent to Trump's Campaign by Paul Erickson, an FBI informant.

https://www.justice.gov/opa/press-release/file/1080766/download

This was five months before the FBI's Carter Page warrant was approved to do the same thing.

https://www.washingtonpost.com/world/national-security/fbi-obtained-fisa-warrant-to-monitor-former-trump-adviser-carter-page/2017/04/11/620192ea-1e0e-11e7-ad74-3a742a6e93a7_story.html?utm_term=.b43edc293518

The source of the "Kremlin Connection" incident is the 99-page report called the "Report on Russian Active Measures dated March 22nd". It is linked here:

https://docs.house.gov/meetings/IG/IG00/20180322/108023/HRPT-115-2.pdf

It was written by nine Democratic Minority Members of the House Permanent Select Committee on Intelligence, headed by Adam Schiff (D-CA).

A copy of Erickson's email is below.