In New Hampshire, he added a stop at the Women’s March in Portsmouth to his schedule and was introduced there by the author Naomi Klein. In Exeter, Mr. Sanders saluted female leaders of the resistance to Mr. Trump and added a promise to his stump speech.

“I want to thank the women of this country for leading the opposition to Trump at every level,” he said. He then vowed: “I will never nominate any individual to the Supreme Court or the federal courts who is not 100 percent pro Roe v. Wade.”

Ms. Warren did not add new remarks about gender in her trip to Iowa, but one of her campaign co-chairs, Representative Deb Haaland of New Mexico, introduced her with a nod toward her history-making potential.

“Elizabeth Warren runs through airports and runs through train stations — she’s a woman on a mission,” Ms. Haaland said. “And if you haven’t heard,” she added, “she’s a woman that will win the White House.”

Ms. Warren’s supporters in Iowa said the episode with Mr. Sanders, which had prompted his supporters to hurl attacks at her online and even refer to her with a snake emoji, was all too reminiscent of his treatment of Hillary Clinton in 2016.

At a Planned Parenthood event with Ms. Warren in Des Moines Saturday, two women mentioned the back and forth with Mr. Sanders and one said that she was getting flashbacks to the last presidential race. One woman asked Ms. Warren what her plans were for “shutting him down and winning his supporters over.” She said Ms. Warren’s disagreement with Mr. Sanders gave her “PTSD” to Mr. Sanders’s feud with Mrs. Clinton in 2016.

“I believe you 100 percent because I looked at you and I looked at him and I thought, ‘He did that,’” the woman told Ms. Warren. “I know Bernie Sanders did those things to you.”