Landmark legislation to reduce the influence of money in US politics won final congressional approval on Wednesday, ending a seven-year struggle on Capitol Hill and drawing a quick vow from President George W. Bush that he will sign it into law.
The Senate passed the legislation, approved five weeks ago by the House of Representatives, on a 60 to 40 vote.
Opponents shifted attention to the courts where they have vowed to challenge the largely Democratic-backed bill on grounds it would violate constitutional guarantees of freedom of speech.
In a written statement a few hours after the Senate vote, Bush said he would sign the measure but called it "flawed in some areas."
"The legislation makes some important progress on the timeliness of disclosure, individual contribution limits and banning soft money from corporations and labor unions, but it does present some legitimate constitutional questions," he said. "I ... believe the best reform is full and timely disclosure of campaign contributions."
Seven years in the making, the campaign finance reform legislation gained momentum earlier this year with the collapse of Enron Corp, which critics say lavished campaign contributions on both Republicans and Democrats to gain access to Capitol Hill and influence policy.
The measure would outlaw hundreds of millions of dollars in unlimited donations, known as "soft money," that have been made in recent years to national political parties.
It would also sharply limit such contributions to state and local political parties, restrict broadcast ads by outside groups shortly before elections and double to US$2,000 the amount of highly regulated "hard money" contributions to individual congressional and presidential candidates.
The measure would implement the biggest overhaul of US campaign finance laws since limits were imposed on donations to candidates a quarter century ago.
But many in both parties remained uncertain about who would eventually benefit most from the changes.
Proponents contend that the bill would help curb big donors from effectively buying access to the halls of power where they can influence legislation.
"Let us take the power away from special interests and give it back to the American people where it belongs," said Senate Majority Leader Tom Daschle, a Democrat.
But a court fight loomed with Senator Mitch McConnell, a Republican and chief congressional foe of the bill, preparing to be the lead plaintiff.
A number of groups have also voiced concerns about the measure, including the the American Civil Liberties Union and the US Chamber of Commerce.
Standing on the Senate floor, McConnell offered a preview of his challenge, which is almost certain to end up in the US Supreme Court.
"I would like to begin by citing the ultimate campaign reform -- the First Amendment to the Constitution: Congress shall make no law ... abridging the freedom of speech," McConnell said.
Senator John McCain, the maverick Republican who made campaign finance reform a centerpiece of his failed 2000 White House bid and brought it to the forefront of the nation's political debate, said he was confident proponents would prevail.
"I think we will do fine in court," McCain said. "I'm not overly concerned, but we have to be prepared."
Up until Senate passage, there had been no official word from the White House on whether Bush would sign the bill. Yet Democrats and Republicans said they expected him to do so.