Not just Congress. The US executive and judicial branches have also never formally recognized dual citizenship.
IOW, any person can be both a US citizen and a citizen of some other country. We just don't recognize the other citizenship and it has no effect at all on his rights or duties as a citizen of this country.
AFAIK, this has been US policy since the Founding.
I'm sure you think this is a bad policy, but it is certainly not a recent one and has nothing to do, in origin anyway, with political correctness.
Well, yes the government does. Hence the term "dual citizenship." If the government didn't recognize the other citizenship, then there would be no such thing as "dual citizenship," as the person would simply be a citizen of the US and only the US, as far as US law is concerned.
My point was that dual citizenship = "natural born US citizen" for constitutional purposes, is not questioned by any member of Congress. IOW, those babies born in the US on the "citizenship vacations," then raised by Korean or Japanese parents, in Korea or Japan, for their entire childhood and young adult life, are (according to Congress) just as much qualified to be president (by dint of being born on US soil), as a child born to US citizen parents.
I believe this policy is new, is enabled by public ignorance, and is an incorrect construction of the US Constitution. Not that the Constitution is worth spit to Congress - just saying, this is another place where the federal government is way out of its bounds.