ANKENY, IOWA (CNN) Elizabeth Warren made a rare direct attack on a Democratic presidential rival Monday, slamming former New York Mayor Michael Bloomberg for spending millions of dollars on ads to "buy the nomination."

"I am here on day two of Michael Bloomberg's $37 million ad buy," Warren said at a community conversation in Ankeny, Iowa, Monday afternoon. "Michael Bloomberg is making a bet about democracy in 2020 -- he doesn't need people, he only needs bags and bags of money. I think Michael Bloomberg is wrong and that's what we need to prove in this election."

Warren's direct attack on Bloomberg illustrates how she plans to use another billionaire's entry into the race as fuel for her candidacy, which is aimed at addressing what Warren sees as a fundamentally unfair economic and political system that benefits the wealthy.

Bloomberg announced he was seeking the Democratic nomination on Sunday and placed at least $37 million worth of television advertising over the next two weeks, according to data from Kantar Media/CMAG.

Instead of campaigning in the early primary and caucus states -- Iowa, New Hampshire, Nevada and South Carolina -- Bloomberg is instead planning on focusing his time and resources in states with larger populations that vote on Super Tuesday.

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