The problem is that Trump is that moderate wing. And he's going to get nuked in the general.
Trump himself is mostly the problem. Some of his positions are desirable to a majority of the public, save for a few like the Muslim ban and the border wall.
As hopper implied (?), the GOP will never recover if they cannot make inroads with minority voters. So far, this looks to be the 3rd straight presidential election where the Republican party has gotten less of the non-white voter than the last election. They are literally approaching single digits, and fast. In a country where non-white voters make up 2% more of the electorate every 4 years, you cannot afford to alienate them like that. Not if you want to win.
So until they moderate more and win over more non-white voters, they will continue to struggle and/or lose.
And if they moderate, it's not like that's a quick fix. They've been too extreme for too long for them to be able to turn it around in the short term. The longer they continue to alienate non-white voters, the longer it'll take them to win them back once they decide to moderate.
