Grassley received whistleblower disclosures alleging that the FBI and DOJ have in their possession an unclassified FD-1023 form that describes an alleged criminal scheme involving then vice-president Biden and a foreign national relating to a quid-pro-quo.
https://www.grassley.senate.gov/imo/media/doc/grassley_comer_to_fbi_-_biden_1023.pdf