Here is just one of many and this particular one is Q/A by a doctor.
“It is a sexual problem, but it is not caused by having your foreskin removed. Please find one web site that says circumcision is the cause of erectile dysfunction. Just one. Oh, and penis enlargement and anti-circumcision web sites don’t count. Find an erectile dysfunction web site that lists causes of ED. Show me one that includes circumcision in the list. “