(Bloomberg) -- Senator Elizabeth Warren is poised to make official on Saturday that she’s mounting a campaign for president.

The Massachusetts Democrat is expected to announce during a speech in Lawrence, a former manufacturing hub in her home state, that she’s seek her party’s nomination to challenge President Donald Trump in 2020. A centerpiece of her campaign will be mitigating income inequality.

Warren set up an exploratory committee on Dec. 31 to consider a run, though there was little doubt she’d follow through with a formal campaign. Since then, she’s sought to correct an early stumble by apologizing to the Cherokee Nation for claiming she’s part Native American.

“While it probably would have been more helpful to respond more quickly after hearing how her response impacted folks in the Native American community, it’s never too late to do the right thing,” said Neil Sroka, a spokesman for the activist group Democracy For America.

Three of her fellow senators also are running -- Kirsten Gillibrand of New York, Kamala Harris of California and Cory Booker of New Jersey -- with others actively considering it. Minnesota Senator Amy Klobuchar is set to announce her plans on Sunday. Warren’s campaign team said she plans to follow the announcement with trips to Iowa, New Hampshire, South Carolina, Georgia, Nevada, and California, early or important states that will help pick the Democratic nominee.

A challenge for Warren, 69, a regular target of Trump’s attacks, is to prove to a Democratic base desperate to defeat Trump that she won’t fail them. In a recent Monmouth University poll, 56 percent of Democrats said they’d prefer a candidate who can defeat the president over one who agrees with them on most issues, while 33 percent said they’d go with a candidate they mostly agree with but would have a harder time defeating Trump.

Closing the gap between the country’s rich and poor, a pursuit of Warren’s that dates back to her time as a Harvard law professor, is set to be a dominant theme of her campaign. She recently unveiled a proposal that pushes the frontier to a new place: directly taxing the very rich. Her new plan would impose an annual 2 percent levy on wealth above $50 million, rising to 3 percent on assets above $1 billion.

“It’s about dealing with extreme concentrations of wealth,” said Stephanie Kelton, a professor at Stony Brook University in New York and former senior economic adviser to the campaign of Senator Bernie Sanders, the Vermont independent who’s considering another run for the Democratic nomination. “There is an awareness that income and wealth inequality has reached levels that Democrats want to interrupt.”

Warren’s said she’d put the revenue raised by a tax on the ultra-wealthy toward programs to cut student debt and expand access to child care.

A survey by Politico/Morning Consult found that Warren’s tax idea is backed by 61 percent of Americans and opposed by 20 percent. Even among Republicans, 50 percent support it while 30 percent oppose it. An Economist/YouGov poll found that 50 percent of Americans support the idea while 23 percent oppose it; among Republicans, 46 percent favor it and 35 percent reject it.

In a presidential field that’s shaping up to be large, Warren’s grasp of pocketbook issues that affect voters is likely to be her main strength in attracting the Democratic activist base.

“In this environment when you have potentially 20 candidates running, everyone’s grasping for that policy that appeals to that most active part of the base, which is the most progressive wing of the base,” said Adrienne Elrod, who served as a spokeswoman for Hillary Clinton’s 2016 campaign.

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