Transcript for 2020 Democratic candidates campaign in Iowa this weekend
Now to the race for 2020. The presidential election one year away. Many democratic candidates in Iowa this weekend. Joe Biden still leading with 28%. Elizabeth Warren rising to 23%. Followed by Bernie Sanders at 17%. And Pete buttigieg at 9%, moving ahead of kamala Harris. Democrats taking aim at each other over medicare for all and how to pay for it. Here's Rachel Scott in Iowa tonight. Reporter: Tonight, facing criticism from her rivals, Elizabeth Warren defending her health care plan, challenging critics to release their own proposals. What is your message to your rivals. If somebody has a better plan to deal with the $11 trillion, that families will pay over the next ten years, they should put it out. Reporter: Warren claims taxes will not go up for the middle class under her plan. Which pulls more than $20.5 trillion in funds for a ten-year period. By calling for new taxes on the wealthiest Americans and corporations. Asking employers to pitch in, too. The math is certainly controversial. There are variations in the estimates in the trillions and trillions and trillions of dollars. And we don't have to go there to deliver health care to everybody. Reporter: Biden's campaign has called the plan mathematical gymnastics. You couldn't even get it passed. Reporter: Bernie Sanders admits that taxes would go up under his plan. But says overall health care costs will go down. I think we have a better way. A 7.5% payroll tax, which is far more, I think, Progressive. Reporter: This battle being fought in Iowa less than 100 days before the caucuses. A new poll shows a four-way race, with buttigieg gaining ground in the hawkeye state. Now in a tight matchup with the other three early front-runners. The strategy going forward is to leave no stone unturned. To try to reach every iowan. Still three months out from Iowa, but the top tier starting to emerge. And Warren's team seeing some encouraging data points in the latest Iowa poll? Reporter: That's right, Elizabeth Warren seems to be in a good place heading into this stretch. She's either the first or the second choice for nearly half of the Iowa Democrats surveyed in the poll. And many of senator Sanders' supporters say, if they had to choose a backup, it would be Warren.
This transcript has been automatically generated and may not be 100% accurate.