Can you always ask for an independent genetic testing when you are asked by the court to support your wife's or your partners children? I am wondering if in the U.S. you can have a court order invalidated after doing a genetic testing to see if you're the biological father, and I am wondering if there's a period after which a court order cannot be invalidated, because I know some people are forced by the law to support children even if they're not genetically related.
Can you always ask for an independent genetic testing when you are asked by the court to support your wife's or your partners children?
No. Only sometimes. (Literally, you can always ask, but sometimes the answer will be clearly "no", as a matter of law.)
Some presumptions of paternity are conclusive (either immediately or after a statute of limitations to contest paternity expires) and can't be overcome by contrary genetic evidence. Other presumptions of paternity are rebuttable. The specifics vary in important details from state to state.
The theory behind the conclusive presumption is primarily that the presumed parent in those circumstances becomes the psychological parent, and it is not in the best interests of the child to dislodge a psychological parent, even if that parent is not a biological parents.
Put another way, a conclusive presumption is really part of the definition of what a father is under the law.