Just wish that a coherent immigration system should have been part of the Founding. The existing slaves could have stayed and given citizenship and immersed into early American culture as soon as possible. But immigration going forward at that time should have been strictly limited to Europe. With a lottery system for the best and brightest everywhere else.
Also of note, is how Obama had a clandestine immigrant plan for African nations while he was in office. Its hard to find any data on the real numbers, but he paved the way for thousands and thousands of Nigerians and other African immigrants. This is totally aside from the Somali and Ethiopians that came in during the past 20 years.