If Trump’s unfavorable were so high he would not be winning the GOP nomination. Its simply untrue.
Presuming 50% GOP and 50% DEM, a candidate requires only 26% of the total to win the majority of their party's nomination votes. Far less to win the plurality. 74% or more of the general electorate could hate them.
Negatives matter far more in the general election than the primary. Hillary for instance also has huge negatives, but she is doing quite well in the DEM primaries.
I realize this is TR now, but self-delusion doesn't win elections. Trump needs to lower his negatives with the general electorate.