For 30 years, lawmakers have wrangled over whether and how to limit the influence of private money in campaigns for federal office. Much of a sweeping 1974 law was ruled an unconstitutional abridgment of free speech. 

What would be the biggest change in campaign finance law since then was passed Monday by the Senate. Here's what led up to it: 

1971 — President Nixon signed legislation establishing in law the use of political action committees funded with voluntary contributions as a means for corporations and unions to contribute to campaigns. 

1972 — The Republican National Committee moved its convention from San Diego to Miami Beach when it was revealed that an antitrust suit against International Telephone and Telegraph was settled out of court around the same time that the company agreed to contribute $400,000 to help cover the costs of the California gathering. Both ITT and the GOP insisted that the two actions were unrelated, but the company's Washington lobbyist, Dita Beard, wrote a memo appearing to acknowledge a quid pro quo. 

1974 — In the wake of the Watergate scandal, Congress passed and President Ford signed a sweeping campaign finance bill. It created the Federal Election Commission, limited individual and PAC contributions to candidates to $1,000 and $5,000 per election, respectively, set spending limits for campaigns and offered partial taxpayer financing to presidential candidates who agreed to limit their spending. 

1976 — The Supreme Court, in Buckley v. Valeo, threw out mandatory limits on candidate spending as a violation of the First Amendment. 

1979 — President Carter signed legislation allowing political parties to raise unlimited "soft money" contributions from individuals, unions and corporations for party-building activities such as get-out-the-vote drives and voter registration campaigns. 

1980 — Republican John Connally became the first major party candidate to run for president without agreeing to limit his spending in exchange for partial federal funding of his campaign. 

1988 — The Republican National Committee set up "Team 100," a roster of contributors who donated at least $100,000 to the party, most of it in soft money. 

1991 — The Federal Election Commission required political parties to disclose for the first time their soft money contributions. 

1992 — President George H.W. Bush, father of the current president, vetoed legislation that would have offered partial public financing to Senate and House candidates who agreed to limit their spending. The Democratic and Republican parties raised $86 million in soft money. 

1994 — The House and Senate passed separate bills. A negotiated compromise reduced what PACs could give to candidates and offered federal subsidies to House and Senate candidates who agreed to limit spending. President Clinton offered to sign the bill, but it died in the Senate to a Republican filibuster on a procedural motion. The two major parties raised $102 million in soft money. 

1996 — Sens. John McCain, R-Ariz., and Russell Feingold, D-Wis., introduced their first campaign finance bill, which would ban PACs and offer financial incentives for candidates to limit spending. The two parties opened a new window on spending, using some of the $262 million in unregulated soft money they raised to pay for ads on behalf of their presidential candidates. Democrats had to return millions of dollars in soft money donations amid allegations they came from foreign sources, which is illegal. 

1998 — McCain and Feingold introduced legislation to ban unlimited soft money contributions. The two major parties raised $224 million in soft money. Members of Congress and potential presidential candidates also raise soft money through their leadership PACs. 

1999 — George W. Bush announced he would forgo partial federal funding for his presidential campaign so he would not have to limit his spending. He later raises a record $100 million and becomes the first major party candidate to win the nomination without following the Watergate-era limits. 

2000 — President Clinton signed legislation requiring tax-exempt political organizations — many of which had spent millions on issue advertisements to help elect or defeat candidates — to regularly report contributions and expenditures. The disclosure requirement also applied to federal lawmakers' leadership PACs. The two major political parties raised close to $500 million in soft money. The Republicans established a new $250,000 category of top givers. Democrats asked the biggest donors for $500,000 each for a one-night fund-raiser last May that took in a record $26.5 million.