(Incidentally, half of the 1992 donations failed, when first disclosed to the FEC, to reveal that the source was a student.)
Students were prohibited from donations, that's why half of them failed.
mnli hypothesis: Students were prohibited from donations, that's why half of them failed. premise: (Incidentally, half of the 1992 donations failed, when first disclosed to the FEC, to reveal that the source was a student.)