Just a few months ago, Republicans were triumphant, while Democrats were demoralized. But something real has happened: Democrats’ fury is building. Perhaps they have had it with Elon Musk. Perhaps Senate Democrats’ capitulation on government funding ignited voters who felt abandoned by their party leaders. Perhaps it was all the institutions cutting deals under pressure from President Trump. Whatever it was, Democrats are proving a political axiom: Anger is a more powerful motivator in voting than happiness and satisfaction.

And Republicans had better watch out, as they learned Tuesday night in a Wisconsin statewide election for a State Supreme Court seat, in which the Democratic-backed candidate prevailed by 10 percentage points just five months after Mr. Trump beat Kamala Harris there by just one point.

As a pollster, I’ve been focused recently on gauging what voters think of Mr. Trump’s performance back in office. One way to do this is by asking if they approve or disapprove of the job he is doing across a range of issues — a metric that in the past few weeks showed gently declining but overall middling approval ratings.

But I think studying how voters feel is also important — maybe even more important than studying what they think. In my polling, when I ask voters how they feel about what the Trump administration is doing, Democrats are not simply dissatisfied. When I offered voters a range of seven emotions in a poll in mid-March, from “furious” to “thrilled,” the top response from Democrats was “furious,” at 38 percent. Only a quarter of Republicans described themselves as “thrilled,” by contrast (though, make no mistake, Republicans support Mr. Trump a great deal).

What should worry Republicans most is that when a party wins elections and its supporters are satisfied with what their side is doing, it becomes easy to rest on one’s laurels and miss the bubbling rage of the other side or not find ways to counter it. Democrats did this, to some extent, during the rise of the Tea Party movement, dismissing it as AstroTurf — activism masquerading as grass-roots energy — and paying dearly for it in the first Obama midterms, in 2010. Republicans may wish to dismiss some of what they see appearing at angry town hall meetings, but this isn’t just the usual anger of an opposition party: Mr. Trump is supercharging the anger in two important ways that add up to even greater potential peril for Republicans in the short run.

The first factor is the nature of Mr. Trump’s policy pushes, such as new tariffs and the mass firings of government employees, which can cause immediate problems for families, consumers and business leaders, with the only balm being his vague assurances of an ensuing upside. This is exactly the kind of dynamic that deepens the frustration and anger of a large group of very personally affected voters, who will seek to send a message.