Republican senator John McCain has joined families of Navajo war veterans who were honoured at the White House in condemning Donald Trump over a "Pocahontas" jibe at a Democratic senator.
The families said they were dumbfounded that the president used the event to take a shot at Elizabeth Warren, demeaning their work with an unbreakable code that helped the US win the Second World War.
Mr Trump had welcomed three Navajo code talkers to the Oval Office, calling them "incredible" and "very special people", but he then added: "We have a representative in Congress who they say was here a long time ago. They call her Pocahontas.
"But you know what, I like you."
The Republican president has repeatedly mocked the Massachusetts senator for claims she has made about being part Native American.
Native American leaders have called Mr Trump's past attacks on Ms Warren offensive and distasteful, and she quickly denounced his comments, saying: "This was supposed to be an event to honour heroes, people who put it all on the line for our country, who, because of their incredible work, saved the lives of countless Americans and our allies.
"It is deeply unfortunate that the president of the United States cannot even make it through a ceremony honouring these heroes without having to throw out a racial slur."
Marty Thompson, whose great-uncle was a Navajo code talker, said: "It was uncalled for.
"He can say what he wants when he's out doing his presidential business among his people, but when it comes to honouring veterans or any kind of people, he needs to grow up and quit saying things like that."
Pocahontas is a well-known historical figure but the National Congress of American Indians says Mr Trump has wrongly flipped the name into a derogatory term.
Arizona Republican senator John McCain, a decorated veteran of the Vietnam War, tweeted: "Our nation owes a debt of gratitude to the Navajo code talkers, whose bravery, skill & tenacity helped secure our decisive victory over tyranny & oppression during WWII. Politicizing these genuine American heroes is an insult to their sacrifice."
White House spokeswoman Sarah Huckabee Sanders said a racial slur "was certainly not the president's intent".
The Navajo Nation suggested Mr Trump's remark was an example of "cultural insensitivity", and they resolved to stay out of the "ongoing feud between the senator and President Trump".
"All tribal nations still battle insensitive references to our people. The prejudice that Native American people face is an unfortunate historical legacy," Navajo Nation president Russell Begaye said in a statement.