Her plan, unveiled in April, proposed eliminating up to $50,000 in student loan debt for every person with a household income of less than $100,000, and canceling a smaller amount for borrowers with a household income between $100,000 and $250,000.

Two months later — in what some Democrats saw as an effort to one-up Ms. Warren — Mr. Sanders came out with his own plan to eliminate all student loan debt .

On K-12 education, Mr. Sanders proposed a detailed plan focused in part on racially integrating schools through measures like busing and increasing funding for magnet schools. He also wants to freeze federal funding for all new charter schools and ban for-profit charter schools. And he proposed big increases in teacher pay and in funding for students with disabilities and schools that serve poor children.

Ms. Warren has not offered a K-12 plan, but she has said that her education secretary would be someone who has been a public-school teacher.

She would get rid of the filibuster. He thinks incarcerated people should get to vote.

In their eagerness to appeal to the activist left, both candidates have taken turns staking out bold positions on once-fringe issues, some of which have become pseudo-litmus tests for the crowded Democratic field.

Ms. Warren, for instance, has called for eliminating the Senate filibuster; Mr. Sanders has expressed reservations about getting rid of it. And Ms. Warren has said she is open to expanding the size of the Supreme Court; Mr. Sanders is not.

Mr. Sanders, on the other hand, has said incarcerated people should be allowed to vote; Ms. Warren supports restoring the right to vote to people after they are released from prison, but she has not backed allowing people in prison to vote.