Trump is learning (slowly) that his strongly-held opinions can turn voters away from him. This country was founded by immigrants, and many of voters are still first or second generation Americans. Too harsh a stand on immigration makes Trump appear paranoid. Stepping back and requiring legal immigration and developing new policies for handling the current illegals, makes him appear to be more of a leader.
Trump wants to build a wall to keep everyone out, then he wants to only keep out some people, then he wants to develop a plan to let people that have been here for a long time stay. He is losing badly, and flip-flopping his views is the only chance his campaign sees in order to win over new voters.
Donald Trump has flipped flopped on his view of illegal immigrants. He initially insisted, several times, that he would have a force to round them up for deportation. He has since said that is not plausible, and he would not do that for long time residents. His position now matches many moderates.
Donald Trump seems to change any stance he takes in order to try to win over a specific group of voters. As of recently Trump had been trying to appeal to Bernie Sanders supporters by trying to sympathize with college students and even support measures that supported the common man, a main focus for the Sander's campaign. Trump doesn't disappoint with his flip flopping mentality when it comes to his stance on Immigration, for his most memorable quote on this is to "build a wall". In case you have been out of touch from society, the wall that is being referred to would be one that is built between the U.S. border and the Mexican border which in addition he openly stated that America should send back anyone of Mexican decent to Mexico; a sentiment shared by millions of his supporters. Although as of recent, Trump has changed stances on immigration, for he has stated that we should send back only the bad ones and that it would be increasingly difficult to send back people who have been here for 15 to 20 years. This change in his political stance, begs the question on whether this a ploy by Trump to gain voters or is there truly a change in this part of his political platform?