This could be a motive for the complaint against Trump because a former official the whistleblower worked closely with was being attacked for foreign policy the whistleblower collaborated on.
The 2020 Democratic candidate with whom the CIA whistleblower had a "professional" tie is Joe Biden, according to intelligence officers and former White House officials.
Michael Atkinson, the Intelligence Community's inspector general, told members of Congress that the whistleblower had a "professional tie" to a 2020 Democratic candidate. He had written earlier that while the whistleblower's complaint was credible, he had shown "some indicia of an arguable political bias ... in favor of a rival political candidate."
A retired CIA officer told the Washington Examiner, “From everything we know about the whistleblower and his work in the executive branch then, there is absolutely no doubt he would have been working with Biden when he was vice president."
As an experienced CIA official on the NSC with the deep knowledge of Ukraine that he demonstrated in his complaint, it is probable that the whistleblower briefed Biden and likely that he accompanied him on Air Force Two during at least one of the six visits the 2020 candidate made to the country.