I think you are confusing Citizens United v FEC (2010) with Buckley v. Valeo (1976). (CU is largely “corporations are people applies in the application of Buckley”.)
Though, also, neither decision impacts limitations on donations to candidates, both address limitations on expenditures (in Buckley’s case by non-candidate persons independent of campaigns, by candidates from personal funds, and by candidates in aggregate; CU mostly deals with the first of those where the legal person is a corporation and not a natural person.)
Though, also, neither decision impacts limitations on donations to candidates, both address limitations on expenditures (in Buckley’s case by non-candidate persons independent of campaigns, by candidates from personal funds, and by candidates in aggregate; CU mostly deals with the first of those where the legal person is a corporation and not a natural person.)