Nearly 650 donors contributed the maximum amount to candidates, PACs and parties in the last election cycle, according to the Center for Responsive Politics.
The court did not heed warnings from Solicitor General Donald Verrilli Jr. and advocates of campaign finance limits that donors would be able to funnel large amounts of money to a favored candidate in the absence of the overall limit.
The Republicans also called on the court to abandon its practice over nearly 40 years of evaluating limits on contributions less skeptically than restrictions on spending.
The differing levels of scrutiny have allowed the court to uphold most contribution limits, because of the potential for corruption in large direct donations to candidates. At the same time, the court has found that independent spending does not pose the same risk of corruption and has applied a higher level of scrutiny to laws that seek to limit spending.
If the court were to drop the distinction between contributions and expenditures, even limits on contributions to individual candidates for Congress, currently $2,600 per election, would be threatened, said Fred Wertheimer, a longtime supporter of stringent campaign finance laws.
The case is McCutcheon v. FEC, 12-536.