But in a series of rulings in recent years, the Roberts court has struck down provisions of federal law aimed at limiting the influence of big donors as unconstitutional curbs on free speech rights.
In the current case, Republican activist Shaun McCutcheon of Hoover, Ala., the national Republican Party and Senate GOP leader McConnell challenged the overall limits on what contributors may give in a two-year federal election cycle. The limits for the current election cycle included a separate $48,600 cap on contributions to all candidates.
McCutcheon gave the symbolically significant amount of $1,776 to 15 candidates for Congress and wanted to give the same amount to 12 others. But doing so would have put him in violation of the cap.
Relatively few Americans play in the big leagues of political giving. Just under 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 when donors make 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.
Associated Press writer Steve Peoples in Boston contributed to this report.
Follow Mark Sherman on Twitter at: @shermancourt