In one corner there is a large group of traders packed in tight and jostling against each other like a crowd of expectant sports fans. They are squashed into the eurodollar pit (this being the impenetrable world of options trading, their activities have nothing to do with euros or dollars).

It was on this spot, on the morning of 19 February 2009, that the modern American revolution began when a short, dapper TV reporter with a loud voice called Rick Santelli went live on CNBC and delivered his famous rant.

He lambasted the Obama administration, then barely days old, for "promoting bad behaviour" by buying up bad mortgages, which he said was merely rewarding "losers".

The traders behind him gave him a mighty roar of approval, the video clip of the rantwent viral on YouTube and the rest was history. Out of it were spawned hundreds of protest groups across the country that have come to be known as Tea Parties.

Twenty months after his rant, Santelli rarely speaks about what happened and is not actively involved in the movement he helped create. But puffing on a smokeless cigarette between his half-hourly broadcasts, he told the Guardian that he'd "never been more proud to be an American" than when he made that speech. "I struck a nerve that people felt so strongly. If the Tea Parties happened because I threw a match into a tinderbox, then I am proud I did it."

What was it about Tea Parties that made him so proud?

"Challenging leaders is as American as it gets. The unique thing about our country is that we don't get behind politicians, politicians get behind us."

The impact of the rise of the Tea Parties is visible even back in Chicago, where it all began. Despite the fact that this is the home of the Obamas, even here their presence is being felt.

Latest polls show that the Democratic candidate for Obama's old senate seat in Illinois, Alexi Giannoulias, is struggling to fend off the challenge of the Republican Mark Kirk. The race, with just two percentage points between them, is extraordinarily close for this heavily left-leaning and union-dominated part of the country.

A recent opinion poll by Rasmussen Reports found that more than one in five respondents from Illinois considered themselves part of the Tea Party movement. Almost half thought the movement good for the country.

The sense that the Earth is moving even in Obama's back yard was palpable in Blackie's Tavern in downtown Chicago on Wednesday night when an impressive turnout of Tea Party followers gathered to share their excitement about the sea-change they believe they are bringing about.

Jeremy Seagal, aged 32, said that by joining the Chicago Tea Party he had created a new social life, hanging out with like-minded people.

When he first signed up back in April 2009 it was a lonely calling. Most of his friends are leftwing and he kept quiet about his attachment. One Facebook friend who learned about his affiliation threatened to beat him up if he ever saw him again.

But Seagal says the mood has changed. "I think people are starting to see that this is not a fringe movement any more, that it's not nerdy or extremist. Now everybody knows I'm a Tea Party member and proud of it."

The tone of the meeting on Wednesday was sober and focused on policy and fiscal issues such as pensions, social security and school choice. The organiser, Steve Stevlic, quipped that everyone should be careful to stay "on message" for the benefit of the CBS News camera that was present, and that when the media had gone home the "real meeting when you can express your hatred" would begin.

Chicago Tea Partiers are hypersensitive about what they see as the media representation of them; they think they are cast as deranged racist extremists.

Dan Proft, a local radio talkshow host, told the gathering that recent polls showed that one in four Democrats did not approve of what he called "Obamacare" – this year's healthcare reforms. "That makes 25% of the Democratic party racist," he joked.

But then there was only one African-American, Jerome Thomas, among the packed bar of about 10 Tea Party supporters, a strikingly low proportion in a city in which black people make up more than a third of the population.

Asked why there was such an overwhelmingly white turnout, Thomas said: "The liberal media want to portray the Tea Parties as racist, but that is misleading. The Tea Party ideas represent the values of all American citizens."

He conceded that in the past conservatives had made little effort to woo African-Americans, "but things are changing, I wholeheartedly believe in that".

The running theme was that the Tea Partiers were sick of paying high taxes, imposed by Democrats and high-spending Republicans alike, and seeing nothing back for it. "In Illinois, they are taxing us more then wasting it, they are taxing us more then stealing it, and we have nothing tangible to show for it," said Nicole Martin.

Kirk Kessler, a salesman, griped that his income this month had been whittled down by about 40% after tax. Was that all it was about then, just a selfish desire to pay less tax? Was a personal desire for more money in your pocket all that the Tea Party was about?

"I'm an individualist. I'm going to spend my money better than the government would spend it. Collectivism will not work in this country," Kessler said.

Put in these terms, the legendary anger of the Tea Party movement, which has spread fear in the hearts of both Democratic and Republican politicians, begins to sound much more like the traditional midterm bickering of a dissatisfied and economically anxious electorate.

"This is America!" Santelli declared, his arms wide open, in the middle of his legendary rant. Maybe so, but looked at from the perspective of Chicago at least, the America he invoked looks remarkably similar to the age-old grumblings of a disgruntled, and white, middle class.