And given that there has been no real enforcement of these rules in the past, fund-raisers haven't lost a lot of sleep about contributions turning out to be tainted.
Fund-raisers have lost a lot of sleep due to improper contributions. 
mnli hypothesis: Fund-raisers have lost a lot of sleep due to improper contributions.  premise: And given that there has been no real enforcement of these rules in the past, fund-raisers haven't lost a lot of sleep about contributions turning out to be tainted.