How did the Federal Election Campaign Act regulate campaign contributions before the McCutcheon ruling?

Before the Supreme Court's ruling in McCutcheon v. Federal Election Commission (2014), the Federal Election Campaign Act (FECA) regulated campaign contributions through two primary mechanisms:

• Base Limits: These were specific caps on the amount an individual could contribute to a single candidate, national party committee, or noncandidate political action committee (PAC) per election or per year.1
• Aggregate Limits: These were cumulative caps on the total amount an individual could contribute to all federal candidates, party committees, and PACs combined during a two-year election cycle.12

While the McCutcheon ruling struck down the aggregate limits as a violation of the First Amendment, it left the base limits intact. Prior to this decision, FECA had been amended several times—notably by the Bipartisan Campaign Reform Act (BCRA) in 2002—to adjust these limits, mandate disclosure of contributions, and address concerns regarding "soft money" and the circumvention of contribution restrictions.234