Harvard Law Professor Elizabeth Warren (D) announced her campaign against Sen. Scott Brown (R-Mass.) this morning via web video.

Warren made the plan official in a statement Tuesday afternoon. Warren is spending the day traveling around the state, starting her first day of campaigning at a subway stop in South Boston where she greeted commuters.

The video is conversational. “I’m going to do this,” she says at the outset, sitting by herself near a window in a blue suit jacket. “I’m going to run for the United States Senate.”

Brown himself is never named; neither is Warren herself. The video is obviously aimed at her supporters. The focus is the middle class, which she says has been “chipped at, hacked at, squeezed and hammered for a generation now, and I don’t think Washington gets it.”

While she has never run for office before, Warren has built up a national group of liberal fans for her work on Capitol Hill. She was chosen by Democrats to chair Congress’s panel overseeing bailout spending, and was tapped by President Obama to help create the Consumer Financial Protection Bureau.

Warren was expected to lead the consumer bureau, which was created last summer. But Republicans in the Senate blocked her nomination.

In Boston, Warren often invoked her controversial role at the congressional oversight panel and the CFPB as a badge of honor.

“I’m willing to throw my body in front of the bus to stop bad ideas” in Washington, she told passerby.

Warren said her tenure in Washington was short compared to the nearly two decades she has lived in Massachusetts and pointed out that her husband is a native.

“I have to prove myself to everybody,” she said.

Several residents said they would support her campaign. One commuter yelled out “We love you! I’m going to volunteer for you, whoo!” Boston resident Sam Chandler said he would vote for Warren because of her history fighting the banks.

“I feel I can trust you,” he said.

Warren tried to play up her middle class roots, stopping by a Dunkin Donuts for a coffee. Her campaign photographer snapped several shots of her greeting workers behind the counter.

“How you holding up?” he asked her.

“Are you kidding? This is fun!” She replied.

“You think this is fun?” he said.

“It’s better than a congressional hearing,” Warren retorted.

Warren does not have a clear path to the nomination; she faces CityYear founder Alan Khazei, activist Bob Massie and Newton Mayor Setti Warren in the primary. Khazei and Warren are both expected to put up a tough fight in what will likely be a very competitive primary. However, Warren can point to a recent poll finding she would fare best against Brown.

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