Many of the administration's immigration actions can be quickly undone by Joe Biden when he becomes president on Jan. 20. Trump's signature border wall went up in environmentally sensitive areas. The Trump administration imposed a freeze in June on new green cards for high-tech workers, seasonal workers and managers of multinational corporations. The administration's many changes to immigration policy make it hard for anyone to plan for the future. “For the most part, the legal immigration system, which is written by Congress, withstood the assaults by the Trump administration,” he said.