Is it legal for a married man in the US to have a concubine with or without the permission of his wife?

In the United States, while polygamy is illegal and not recognized, a married man can have a concubine, but this can lead to legal and social complications. If the wife consents to the arrangement, it may be more socially acceptable, but it can still impact divorce proceedings, custody, and other legal matters. Without the wife's consent, the situation could lead to issues such as claims of adultery or emotional distress. Ultimately, legality varies by state, and it's advisable to consult legal experts for specific circumstances.