Slipping

Why are minorities suddenly entitled to jobs and platforms and Oscar nominations that previously belonged exclusively to whites? Trump’s supporters see their social status slipping at others’ expense in what they perceive to be a zero-sum game. And they may not be wrong.
Molly Ball. The Resentment Powering Trump

While I suspect that, given the general context of her article, that Ms. Ball meant to say that Mr. Trump's supporters see their social status slipping for others' benefit, the idea that they perceive society and social advantage to be zero-sum is likely dead on. Because that is the nature of status.

Imagine a group of people picking apples, and they are being ranked on the number of apples they pick. Let's say that Jack is an apple-picker, and the first time the number of apples picked is measured, Jack scores a respectable 50 apples. Jill is also picking apples, and at the first measurement, she picks 30 apples. By this measure, Jack ranks above Jill, and enjoys the status thereof. After reforms to the apple-picking process are made, there is another round of picking, and another count. This time, Jack picks 65 apples, and Jill 70. If we measure apples as income, both of them are better off. And the total number of apples picked is greater making the over all pie (ahem) bigger. But despite the fact that Jack has done significantly better than he had done before, status-wise he's losing out to Jill, because she picked more apples. And to the degree that certain advantages are conferred on group members due to their ranking as pickers, rather than simply being a direct function of the number of apples they pick Jack loses access to advantages that Jill gains. And if inflation eats into the buying power of Jack's apples, he can easily feel himself objectively worse off than he had been before. And to the degree that Jack felt that his earlier apple-picking superiority was due to his hard work and Jill's laziness, rather than processes that advantaged him at Jill's expense, it's easy to understand that Jack might concluded that the reforms put in place were stacked against him, perhaps deliberately.

Advantage is difficult to see for people when it's simply the way the world has always worked. For many people, Jim Crow was a long time ago, and the minute after the last racist law was repealed, the world suddenly became a complete meritocracy, regardless of the fact that the same people who had presided over the old order were still around, and laws can't change attitudes.