As the court reasoned in 1976, the message implicit in a campaign contribution--I support Candidate X--has little to do with the size of the contribution.
The court decided that support has little to do with contribution size. 
mnli hypothesis: The court decided that support has little to do with contribution size.  premise: As the court reasoned in 1976, the message implicit in a campaign contribution--I support Candidate X--has little to do with the size of the contribution.