She called herself the “warm-up act” for Bill Clinton at the Democratic Convention, but Elizabeth Warren electrified the crowd by delivering the fierce heat of the truth straight from the heart:

“People feel like the system is rigged against them. And here’s the painful part: they’re right. The system is rigged. Look around. Oil companies guzzle down billions in subsidies. Billionaires pay lower tax rates than their secretaries. Wall Street CEOs — the same ones who wrecked our economy and destroyed millions of jobs — still strut around Congress, no shame, demanding favors and acting like we should thank them. Anyone here have a problem with that? Well I do.”

Running for the Senate against a popular incumbent in Massachusetts, Warren is an unlikely candidate. She’s a Harvard law professor, and looks the part with her glasses and no nonsense hair, and sounds it as she speaks naturally in full paragraphs, not sound bites. She made her name studying bankruptcy laws, and exposing how that system was rigged against the struggling middle class families who hit the wall after an illness or the loss of a job.

As chair of the Congressional Oversight Panel for the Troubled Asset Relief Program, the Wall Street bailout, she infuriated the big banks and Treasury Secretary Tim Geithner by questioning why the banks were getting a free pass and wanting to know where the money went. She championed the creation of the Consumer Financial Protection Bureau, overcoming resistance in the Treasury Department and frontal assault by the banking lobby, to get it through Congress as part of President Obama’s financial reforms. Treasury retaliated by blocking her appointment to head the bureau she created. The Senate run was a way to stay in the fight for working families who aren’t getting a fair shake.

Throughout the campaign, Warren has delivered an unabashed populist message. She first made the common sense case that no one succeeds alone; that successful businesspeople depend on what we’ve built together — an educated workforce, roads and transport to deliver their products, a rule of law vital to working markets. This isn’t a radical notion, but when adopted and badly phrased by President Obama, it sparked the frenzied Republican “we built it” campaign.

After the Democratic convention, polls showed Warren emerging with a small lead over incumbent Sen. Scott Brown. Unseating Brown is no easy task. Brown campaigns as a sunny, likeable “nice guy with a truck,” but is skilled at back alley political knife fights. Massachusetts has a record of supporting Republican moderates and is notoriously tough on female candidates. Warren isn’t a natural fit.

Brown is slick, trying to have it both ways. He calls himself the “second most bipartisan Senator” in the Senate, while Fortune Magazine more accurately called him “Wall Street’s favorite candidate.” He runs as the protector of small business, while pocketing cash from Wall Street bankers apoplectic at the idea of a Warren victory. He runs as far from the Republican label as possible in Massachusetts, while cashing big checks from deep pocket Republicans across the country, who argue that his victory is vital to if Republicans are to take the Senate.

Their first debate offered voters a revealing contrast. Brown, shedding his nice guy persona, opened the debate attacking “Professor Warren’s” character for “checking the box” claiming her native American heritage on her employment form, although it made no difference in her hiring by Harvard. He responded to a question about the cost of college by braying against her “$350,000 salary for teaching one course,” as if her salary was driving up the costs of college.

Warren responded by focusing on Brown’s voting record in favor of billions in subsidies to Big Oil, against raising taxes on billionaires and against closing corporate loopholes to pay for sustaining lower interest rates on student loans.

Perhaps the most revealing moment came in response to a question about the coming “fiscal cliff,” and what should be done about it. Brown likes to posture tough on deficits, while calling for even more top end tax cuts. He invoked the “bipartisan approach,” ignoring the fact that any bipartisan approach must require some of the tax hikes he opposes.

Warren cut through the bull. What we need, she said, is a “balanced approach.” Yes, we’ve got to cut some spending — agricultural subsidies, cuts in the Pentagon’s budget, end the war in Afghanistan, go after waste and abuse. But we’ve also got to ask the wealthy and the big corporations to pay their fair share of taxes. “Senator Brown has voted against this.”

Warren still faces forbidding odds. Wall Street’s favorite will campaign as a champion of the little guy while painting Warren as an elite Harvard professor who just wants to raise taxes.

Warren will focus on the core issues, and ask Massachusetts’ voters to decide who is on their side. And if she wins — hopefully joined by Sen. Sherrod Brown in Ohio and perhaps Rep. Tammy Baldwin in Wisconsin — she’ll not only lead a new generation of progressive reformers into the Senate, but also begin to teach Democrats how to fight for working people once more.