Here are 3 previously unthinkable ideas Elizabeth Warren thrust into the mainstream before ending her presidential campaign

Warren was the first major presidential candidate to propose canceling a substantial portion of student debt in the US, unveiling the plan last year.

She called to make two-year and four-year colleges and universities free for people so they wouldn't be "paying a dime in tuition or fees." The proposal carried a price tag of $610 billion.

Her $640 billion loan forgiveness plan would have slashed up to $50,000 in debt for student loan borrowers making less than $100,000. It also sought to gradually forgive debt for people earning up to $250,000. Both proposals — totaling $1.25 billion — were paid for by the wealth tax.

Sanders followed up with a student debt plan of his own that wiped it out entirely by way of a new tax on Wall Street, escalating the policy duel between them.

Then in January, Warren put forward another plan laying out how she would achieve her student-loan objectives, mainly by empowering the Education Department and sidestepping Congress.

Federal data shows that the share of student debt has doubled over the past decade from $700 billion to $1.6 trillion, overtaking credit cards and car loans as the largest share of debt held by 45 million Americans. The average college student graduates with at least $30,000 in debt, CNBC reported.

A Quinnipiac poll last year found that 57% of Americans backed Warren's student loan policies.

Early last year, Warren rolled out a plan aimed at making childcare both affordable and easy to access for parents. She wanted to create a network of facilities to take care of children that the federal government subsidized and regulated.

"There are two big problems with child care in America: it's hard to find high-quality care, and where you do find it, that care is extraordinarily expensive," she wrote in the proposal, noting that care for one child could cost anywhere from 9% to 36% of a family's total income.

Child care would have been free to any family earning below 200% of the federal poverty line. For families over that threshold, the cost would be capped at 7% of their income.

The government currently provides some assistance for low-income families with children, and working parents can benefit from a child-care tax credit.

But half of Americans reside in communities with no licensed care provider for children or contend with a vast shortage of available slots, according to the Center for American Progress, which called these areas "child care deserts."