"We'll see how she does", he said.
"This is an America that is working for those at the top and not anyone else, and that is why I'm here", Warren said at a Friday evening event in Council Bluffs, Iowa, the first of five back-to-back speeches and meet-and-greets with voters planned for the weekend.
"We've got to stand behind the kinds of changes that will matter in the lives of everyday people..." Her first speech was in the western part of the state where she sounded like she was on the campaign trail.
Warren insisted that according to "family lore", at least one of her ancestors was a Native American.
"As you came in, there was a cage of women, another cage of women packed in, cages of men", she related. "I'd love to run against her".
Massachusetts Sen. Elizabeth Warren has hired Barack Obama's former chief digital strategist to help lead her emerging 2020 presidential campaign and has also recruited a Democratic operative with deep experience in Southern politics ahead of a long primary.
Her call for billionaires not to self-fund campaign operations follows CNBC's reporting that Democratic donor and former New York City Mayor Mike Bloomberg was prepared to spend more than $100 million on his own campaign organization if he were to run in 2020.More news: Baker Mayfield fined $10K for 'lewd' TD celebration, report says
"I think that campaigns should not be for sale", she said.
Warren was scheduled to hold public events in western Iowa Friday evening and Saturday morning, and appear in Des Moines for a gathering on Saturday evening.
Warren has had a rough start to her presidential bid all around. Elizabeth Warren watches her carbs and calories even when hitting the sauce.
A better-than-expected finish in Iowa could position Warren well in New Hampshire, where she would be expected to perform well as a neighbor to the first-in-the-nation primary state.
Warren's mantra has been that she wants to make changes to the federal government that now "works great for the wealthy and the well-connected" but leaves millions of other Americans out in the cold. Bernie Sanders, I-Vermont, another likely 2020 presidential contender.
Hillary Clinton in 2016 launched a similar "listening tour" that took her to early states.