Less publicized trends among key demographic groups are compounding Republican anxiety. Trump’s heaviest losses, according to survey data, are among those voters he most needs to remain competitive: whites and especially white men.

When you compare polls taken between May 22 and 25 (the high point to date for Trump in matchups with Hillary Clinton) with polls published over the last week, you can see how much damage Trump has inflicted on himself. In matchups with Clinton, Trump has experienced double digit declines in support from men, from young voters, from all whites and from white college graduates in particular.

Polls are also showing an increase in the percentage of Republicans who are indicating that they might sit out the 2016 election. The Reuters-Ipsos tracking poll measures how many voters refuse to say whether or how they will vote. Among Republicans, the percentage of these voters has risen since early May from 17.2 percent to 26.6 percent. Among Democrats, the percentage has remained relatively constant, fluctuating between 19 and 21 percent.

There are other recent measures of Republican disaffection and Democratic enthusiasm.

A Marquette Law School survey of Wisconsin voters, published on June 15, shows that among Democrats an increasing number of people are committing to vote in November — from 80 percent in March to 84 percent in June — while the percentage of Republicans committed to voting fell from 87 percent to 78 percent over the same time period.

Trump may well have contributed to declining excitement among Republican voters when, at a rally in Atlanta on June 15, he unleashed a frenzied attack on Republican leaders:

You know the Republicans — honestly folks, our leaders, our leaders have to get tougher. This is too tough to do it alone, but you know what I think I’m going to be forced to. I think I’m going to be forced to. Our leaders have to get a lot tougher. And be quiet. Just please be quiet. Don’t talk. Please be quiet. Just be quiet to the leaders because they have to get tougher, they have to get sharper, they have to get smarter. We have to have our Republicans either stick together or let me just do it by myself. I’ll do very well. I’m going to do very well. O.K.? I’m going to do very well. A lot of people thought I should do that anyway but I’ll just do it very nicely by myself.

Paul Ryan, asked to comment on Trump’s remarks, laughed incredulously and said, “You can’t make this up sometimes.”

As Trump becomes the indelible image of the Republican Party, the problems for Republican candidates seeking to distance themselves from him are only going to worsen. Trump’s imprint on the party will be cemented in the minds of many voters during the convention in Cleveland from July 18-21, which Trump intends to turn into a four-day spectacle focused on his persona — an entertainment extravaganza designed to hold millions of voters to their television (and other) screens.

If Trump’s poll numbers continue to slide, Clinton is positioned to damage his campaign before the general election is fully engaged. She has already begun an attempt to do so: Clinton and allied groups have so far spent $26 million on television ads, many of them featuring hard-nosed anti-Trump attacks, while Trump has aired no ads over the past month.