Under Presidents Obama, Bush and Clinton, median income in the U.S. has not gone up in more than 15 years. There are currently many people in the country suffering from unemployment or underemployment.
Donald Trump believes these people should not be burdened with further difficulty in finding a job due to illegal immigration on the scale of that which is currently taking place under President Obama and that which has been proposed by Hillary Clinton. Donald Trump has always been clear about his policy on immigration; he wants people to have the right to immigrate to the United States, but they must come in legally.
Trump believes that immigrants who commit crimes should be deported IMMEDIATELY and that all immigrants seeking to enter the U.S. should be subject to extreme vetting before they are allowed to come in. Trump will build a strong, thick and high wall to keep illegals out and fortify it in a way that puts walls at the current border to shame.