"These code talkers deserve our nation's praise and gratitude, not a president who disrespects the Native American community and dishonors Native American veterans", Democratic National Committee Chair Tom Perez said in a statement Monday.
When asked whether it was a racial slur, Sanders said that was "ridiculous".
The president has frequently called Warren "Pocahontas" as a jab at her self-proclaimed Native American ancestry.
Look, is it amusing that Warren once claimed Native American heritage?
"The President certainly (has) an extreme amount of value and respect for these individuals, which is why he spent time. honoring them today", she continued.
I want to build a wall around the White House that doesn't allow anyone of color inside, because once inside we can't keep you safe.
President Trump on Monday revived his favorite nickname for Sen. "And from the heart, from the absolute heart, we appreciate what you've done, how you've done it, the bravery that you displayed, and the love that you have for your country".
Trump said: "We have a representative in Congress who they say was here a long time ago". World War II Navajo Code Talker and Iwo Jima survivor Thomas Begay is one of the last surviving code talkers.
White House Spokeswoman Sarah Sanders, responding to questions from reporters Monday, said she didn't believe calling Warren "Pocahontas" was a slur.
"It is deeply unfortunate that the president of the United States can not even make it through a ceremony honouring these heroes without having to throw out a racial slur". Donald Trump does this over and over thinking somehow he is going to shut me up with it. Warren says she did this to try to meet people of similar heritage. "The prejudice that Native American people face is an unfortunate historical legacy", Begaye said. Scott Brown (R), the Boston Herald found that she was listed as a "minority law teacher" in law school directories from the Association of American Law Schools from 1986 to 1995.
"I've seen men and women of all ages break down in tears in honor and in awe of meeting them in person and they subsequently share their personal or family stories about how the Code Talkers affected their lives".More news: Melania Fires Back at Vanity Fair: I'm 'Honored' to Be First Lady