Given his coalition, his initial statement on that amendment was stupid. He initially said he was going to vote for an amendment, in Florida, with zero abortion restrictions. It is currently six weeks. Now he may feel that six weeks is too little (he said as much) but to turn around and throw his name behind an amendment that would have next to no restrictions was just stupid. Even if that is his position, it is not the position of a core group of his constituency. They (rightfully) felt it was a stab in the back. It has been walked back at this point, we'll see how much damage was done.
There is a group of people that are all in on Trump, almost no matter what he does. I don't know how large that group is. I get the feeling that he thinks it is really big. I tend to think that most people are like me. This is currently an inconvenient marriage and he is the choice by being better than the alternative. As he continues to shift to the left, the gulf between those choices becomes smaller, and all the bull shit you have to put up with to continue to support them becomes harder to swallow. Lila Rose fired a shot across his bow on the abortion thing. The social conservatives are the only leg on the stool he has left mostly unmolested. I don't think he can chop down all 4 and expect to win in November.
In reference to the legs, I think there are 3 to 4 areas that have mostly defined the GOP coalition in my lifetime: Economic Conservatives, NeoCons/Foreign Policy Conservatives, Social Conservatives, and Libertarians. I think people tend to have opinions on all of those things but for many, one of them is their deal killer identity. Trump has done or said things to hurt himself with all 4 constituencies. I think worst damage to the Foreign Policy/Neocon group. His abortion stance this past week would have wrecked him with the social conservatives. He still would probably get quite a few of them to vote for him, but I think enough of them would throw their hands up in exasperation with him and just stay home that it would cost him any chance he had with the election. I don't think the percentage of people that are slavishly devoted to him is anywhere near what Democrats believe it is.