Just days after taking her first formal step toward a 2020 presidential run, Sen. Elizabeth Warren took aim at President Trump, saying he is an "accelerant for corruption" and calling his presidency "one grift after another."

"I want to be in this fight," Warren told Rachel Maddow on MSNBC Wednesday.

"This is truly about what kind of country we are going to be. I never thought I would get into politics, not in a million years, but I got in this because I believe this is the fight that we must fight, and I can't tell others to go fight it. I have to be in there right alongside them."

Warren announced last Monday she was forming an exploratory committee ahead of a possible White House bid in 2020.

On "America's Newsroom" Thursday, Wall Street Journal editorial page assistant editor James Freeman said Warren essentially ended her chances at winning the presidency with her claims about having Native American heritage.

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Trump and others have suggested that Warren claimed Native American ancestry to advance her career as a professor at Harvard University.

In response, Warren released DNA test results in October, revealing that she likely has a Native American ancestor dating back six to 10 generations, which would make her between 1/64 and 1/1,024 Native American.

Critics have pointed out that would make Warren less Native American than the average European American. And Trump -- who has repeatedly mocked Warren with the nickname "Pocahontas" -- took another shot at her ancestry claims on Twitter Thursday.

"If you accept her as a Democrat, you accept that identity politics ... is kind of a fraud and a partisan tool that you just trot out as necessary, but ignore when one of your own goes around claiming for years to be part of a minority group and then reveals that she isn't," Freeman said.

FoxNews.com columnist Liz Peek said Warren also has a tough road ahead on policy, as she is primarily known for her stance on wealth inequality and financial industry regulation.

"I don't think she's actually going to be able to broaden her platform in a totally acceptable way," Peek said.

She noted, however, that Warren's energy and passion are undeniable, even if the Massachusetts Democrat's beer-drinking Instagram livestream came across as "phony baloney."

Watch the panel discussion above.

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