reported on Congress for the New York Times and is now an author and investment banker in Philadelphia

Now that Al Franken has been sworn in as Minnesota's new senator, Senate Democrats finally have the 60 votes they need to stop the GOP's last major weapon: the filibuster. If they can get those votes when they need them, it will bring about a major shift in American politics.

For two centuries, this parliamentary maneuver, unique to the United States, has allowed any senator to delay action for as long as he or she could keep talking on the Senate floor or, with the support of 40 percent of the Senate (33 percent before 1975), kill a bill or nomination. From Jimmy Stewart's battle to stop a crooked land-development bill in Mr. Smith Goes to Washington to an episode of The West Wing where a 10-hour filibuster won $47 million to fight autism, the filibuster has been portrayed as a key safeguard of minority interests. Its importance has especially increased in recent years.

The first filibuster was in 1837, although Senate rules had allowed unlimited debate since 1806. Opponents of President Andrew Jackson vowed to talk until the Senate adjourned, hoping to block a move to expunge an 1834 resolution that had censured him for trying to kill the Second Bank of the United States. Jackson's supporters "fortif[ied] themselves with an ample supply, in a nearby room, of cold hams, turkeys, beef, pickles, wines and hot coffee." The attempt failed and the resolution was expunged.

Filibusters were rarely used during the next 80 years, until a national uproar sparked the first rule to stop them. After German submarines resumed attacks on ships headed for Britain, President Woodrow Wilson introduced a bill to arm U.S. merchant vessels. Eleven senators, fearing it would lead to war, filibustered until Congress adjourned on March 4, 1917.

The release of a telegram revealing that Germany had invited Mexico into an alliance to seize Texas, New Mexico, and Arizona sparked national outrage and Wilson demanded action. "A little group of willful men, representing no opinion but their own, have rendered the great government of the United States helpless and contemptible," he said. There were protests and postings of "rolls of dishonor;" one state legislature denounced the delay as "little short of treason," and another called the filibustering senators "unmanly, unpatriotic [and] un-American."

Reaction to those supporting the filibuster was intense. University of Illinois students hung Sen. Robert LaFollette in effigy; state residents delivered 30 pieces of silver to Arkansas Sen. William Kirby, declaring "if Judas Iscariot earned his, so have you," and voters sent a large iron cross inscribed "Lest the Kaiser Forget" to Mississippi Sen. James Vardaman.

Congress quickly reconvened and the Senate voted 76-3 that two-thirds of those present and voting could invoke "cloture" to close down debate. That limited filibusters but also institutionalized them, since a two-thirds majority would be needed to change Senate rules. Cloture was invoked for the first time in November 1919, ending a filibuster on the Treaty of Versailles.

Despite cloture, dozens of filibusters were used to block civil rights legislation over the next 50 years, including a record-setting 24 hours and 13 minute marathon in 1957 by South Carolina Sen. Strom Thurmond (even longer than Stewart's cinematic effort). The Civil Rights Act of 1964 endured a 57-day filibuster before it was passed.

In March 1975 a bloc of liberal senators won a favorable ruling from Vice President Nelson Rockefeller (in his role as president of the Senate) that enabled them, after decades of failed efforts, to cut cloture from two-thirds to three-fifths. But Southern conservatives weakened that change to require three-fifths of the full Senate (60 of 100 senators), not just those present and voting. They also ensured that any further changes to the cloture rule would need a two-thirds majority.

By the mid-1980s actual filibusters were rare, but the political leverage of a filibuster threat became a common tactic whether Democrats or Republicans were in the minority. Before 1970 no two-year Congress ever saw more than seven cloture motions. Filibuster threats then started to dramatically rise, hitting a record of 139 cloture motions in the 2007-08 Congress and blocking most controversial legislation or contentious nominees.

After Democrats blocked votes on President Bush's judicial nominees in 2005, the Senate's GOP leaders threatened to abolish the filibuster. Sen. John McCain led the bipartisan "Gang of 14" that pledged not to kill it if votes were allowed on most nominees. Sen. Barack Obama did not join them and told the St. Louis Post-Dispatch: "I'm not a huge fan of the filibuster. Historically, what was it used for? Keeping me [African Americans] out of polling places."

The power of a filibuster threat was demonstrated again this February, when Obama and the Democrats had to make significant concessions in their stimulus bill to gain the support of Sen. Arlen Specter, before he switched parties, as well as Maine GOP Sens. Susan Collins and Olympia Snowe. The seating of Franken now means the Republicans have lost their last tactic to block the Democrats' agenda.

In the 92 years since the start of cloture, Senate Democrats have had filibuster-proof majorities three times - 1935-43, 1965-67 and 1975-79 (the GOP has never reached that level). But those majorities were before a filibuster threat became a key tool in an acrimoniously divided capital.

Democrats will need to keep all their members, and those who vote with them, united, and that may be difficult to consistently achieve. Specter, for example, voted against the administration's budget resolution and may not be consistently reliable. Yet the ability to shut down Senate debate on most bills and nominations, plus Democratic control of Capitol Hill and 1600 Pennsylvania Avenue, will be a concentration of power rarely seen in Washington.

The election of the nation's first African American president was a landmark political event. The end of the filibuster's power will bring an even greater change to American politics.