The reliability of polls broke down over the last few years due to: 1) lack of standard ways of contacting people being polled since in stead of everyone having a landline phone, people have diverse ways of being contacted; 2) mass media become highly politicized, since people being being polled tend to give the “right” answer to the pollster regardless of who they plan to vote for, and the mass media are overwhelming “blue” (Fox and the WSJ tend towards purple, nothing tends solid red until you get to specialized sources such as Breibart).
Given the historic trend of presidents who manage to crash the economy being defeated for reelection (“it’s the economy stupid”), Trump probably is in big trouble. Regardless of what media say, people ask themselves if they are better off than four years ago, and for most people the answer is “no”, and especially among the working class voters who are the core of Trump’s base.