Democratic Senator Elizabeth Warren, a strong critic of Donald Trump, has taken a major step towards a likely run for the presidency, seeking to upset the incumbent Republican in 2020.
The 69-year-old, who has represented Massachusetts in the Senate since 2013, is a progressive Democrat.
She said she was launching an exploratory committee for president, which would help her raise funds early in the campaign cycle.
"America's middle class is under attack," she said in a video message on Twitter.
"How did we get here? Billionaires and big corporations decided they wanted more of the pie, and they enlisted politicians to cut them a fatter slice."
"Every person in America should be able to work hard, play by the same set of rules, & take care of themselves & the people they love," she said.
"That's what I'm fighting for, & that's why I'm launching an exploratory committee for president. I need you with me."
Ms Warren has been a frequent sparring partner for Mr Trump, who has repeatedly mocked her claim to have Native American heritage by calling her "Pocahontas," which has been taken as a slur.
Pocahontas was a Native American woman who lived in the 17th Century and is known in US history for her encounters with colonial settlers in Jamestown, in what is now Virginia.
