THE filibuster — tool of obstruction in the US Senate — is alternately blamed and praised for wilting President Barack Obama’s ambitious agenda. Some even say it’s made the nation ungovernable.

Maybe, maybe not. Obama’s term still has three years to run.

More certain, however, is that Opposition Republicans are using the delaying tactic at a record-setting pace.

“The numbers are astonishing in this Congress,” said Jim Riddlesperger, political science professor at Texas Christian University in Fort Worth.

The filibuster, using seemingly endless debate to block legislative action, has become entrenched like a dandelion tap root in the midst of the shrill partisanship gripping Washington.

But the filibuster is nothing new. Its use dates to the mists of Senate history, but until the civil rights era it was rarely used.

A tactic unique to the Senate, the filibuster means a simple majority guarantees nothing when it comes to passing laws.

“The rules of the Senate are designed to give muscle to the minority,” said Senate historian Donald Ritchie.

With the Senate now made up of 100 members, two for each of the 50 states, an opposition filibuster can only be broken with 60 votes — a three-fifths majority.

As a matter of political philosophy, the concept of the filibuster arises from a deep-seated, historic concern among Americans that the minority not be steamrolled by the majority.

It is a brake and protective device rooted in the same US political sensibility that gave each state two senators regardless of population.

The same impulse gave Americans the Electoral College in presidential contests — a structure from earliest US history designed to give smaller population states greater influence in choosing the nation’s leader.

Given the recent use of the filibuster by minority Republicans and the party’s success in snarling the legislative process in this Congress, Democrats say the minority has gone way beyond just protecting its interests.

The frequency of filibusters — plus threats to use them — are measured by the number of times the upper chamber votes on cloture. Such votes test the majority’s ability to hold together 60 members to break a filibuster.

In the 110th Congress of 2007-2008, with Republicans in the minority, there were a record 112 cloture votes. In the current session of Congress — the 111th — for all of 2009 and the first two months of 2010 the number already exceeds 40. The most the filibuster has been used when Democrats were in the minority was 58 times in the 106th Congress of 1999-2000.

During most of Obama’s first year in office and for a few weeks this year, 58 Democratic senators and two Independents who normally vote with them held a filibuster-proof 60-seat majority in the Senate.

That vanished last month when Massachusetts Republican Scott Brown captured the seat of the late Senator Ted Kennedy, who died last summer.

Most notably, Brown’s victory has stymied Obama’s push to overhaul health care just as the bill was approaching the finish line. Before Brown’s election, both the Senate and the House of Representatives had passed separate versions of the reform legislation.

Brown broke the Democratic 60-seat majority before the two chambers could meld differences in their bills for a final vote in both houses.

However, one of Brown’s first votes after taking office saw him joining four other Republicans to help Democrats break a threatened filibuster by his party’s leaders against a job bill.

The measure, $13 billion in tax incentives for businesses to hire unemployed workers, was quickly passed the next day with 12 Republicans joining Brown and 55 Democrats in favour of it.

Filibusters to make the Obama administration and Democrats in Congress look inept are one thing. Quite another is a vote against creating jobs in an economy with nearly 10 per cent unemployment and mid-term elections nine months away.