The use of the expression "undocumented immigrant" by President Harrison is unfortunate. There is no such a class of people. If you drive without a driver's license, you are not an "undocumented driver". If you practice medicine in this country without a license, you are not an "undocumented physician". If you fly a commercial airliner without a license, you are not an "undocumented pilot". All of that is illegal, as it requires proper government authorization in the form of a license. Immigrating to this country, or any country, also requires government authorization. It is called a Visa. It is the law. If you do not have it, you are an illegal immigrant, there is no other way to say it.