While the FEC sets limits on how much a political party or PAC can spend on individual candidates, unlimited amounts of soft money can be spent by political parties, PACs or issue advocacy groups as long as that money is not spent in support of or against particular candidates.

"We cannot advocate the election or defeat of a specific candidate," said Tom Lu, a Republican National Committee spokesperson. "We can point out differences in positions."

This minor technicality provides a huge loophole for candidates and contributors as unlimited amounts of money can be raised and spent on television campaigns, for example.

"Soft money is one of the biggest loopholes that special interests have to get money to campaigns," said Eric Schmeltzer, communications associate at Public Campaign, a not-for-profit organization advocating campaign finance reform. "It is one of the biggest sources of buying influence and access to elected officials."

But if McCain and Bradley want to build support for their presidential bids using campaign finance reform as a central issue, they must be able to explain the rather technical legal issue in ways voters can understand.

In his speech on Wednesday, McCain tried to describe the problem in simple terms, by taking jibes at Gore and President Clinton.

"Most Americans care very much that the Lincoln bedroom has become a Motel 6 where the President of the United States serves as a bellhop," he said. "Most Americans care very much when monks and nuns abandon their vows of poverty and pay tens of thousands of dollars to have spiritual communion with the Vice President."

He cited the tax system as an example of the direct influence special interests can gain through contributions.