It does not, and it never has.
It is a twisted way of saying multi-cultures being tolerated.
A closer look to immigration of masses shows that very few Melt in, or adopt. Most either set up a Ghetto (Chinatown, Polish town or Germantown, or Little Italy conclaves.) Minnesota for example is/was
primarily a grouping of White, Lutheran, Nordics (birds of a feather flock together) Just as the "Pennsylvania" Deutsch
It was/is believed that many persons have entered the country to destroy it from the inside, while becoming citizens or acting like citizens are truely still loyal to their homeland, or worse adverse political thinking. (aka Moles, Agents Provocateurs, .inside agent, etc.)