Everybody has their own idea about the one message Democrats should use against President Trump, the one argument that will pull over the maximum number of voters and ensure the president’s defeat. The truth is that there isn’t just one, and never is. There are always plenty of critiques one can make of the other side.

But if they’re looking to put one at the top of the list, there’s no single attack that works better than this one: Trump and Republicans are serving the wealthy and powerful at the expense of everyone else.

It’s an oldie but a goodie, and sometimes I marvel about the fact that any Democrat ever stops talking about it. Consider this from The Post’s Tory Newmyer:

Democratic pollster Celinda Lake says the Trump cuts, whose second anniversary arrives this month, present a ripe target for Democrats to make the case the president has betrayed the populist pitch he made in 2016. She tells me focus groups she’s conducted with disaffected Trump voters reveal they are “really, really mad” about the corporate windfall the cuts yielded, “and a remarkable number of people know about companies like Amazon that aren’t paying any taxes.”

The public has misconceptions about a lot of things, but this is an area where they understand reality quite well. There has in fact been a huge increase in inequality in recent years. The rich do in fact manage to avoid paying what they should, and the richer they are, the better they are at avoiding taxes. The system is indeed rigged by and for the interests of corporations and the wealthy.

Which is why, if you look at polling on the subject of taxes, huge majorities consistently say that the rich and corporations pay too little. In Pew polling, over 80 percent of people say they’re bothered by corporations and the wealthy not paying their fair share. In a Politico/Morning Consult poll, 76 percent say the rich should pay more.

The same goes for specific proposals. Take a wealth tax of the kind Elizabeth Warren has advocated. There are legitimate critiques you can make of it — it would be difficult to enforce without an enormous increase in IRS agents (which we need anyway, but that’s another story), there are other ways to get the revenue, and so on.

But the fact remains that a wealth tax is hugely popular, with 60 percent or more of the public saying they support it.

Or a financial transaction tax on Wall Street, in which a small tax would be assessed every time a trade is made. A number of Democratic candidates support the idea, which according to this Brookings Institution analysis could raise up to $75 billion a year; 75 percent of the burden would fall on the top income quintile, and 40 percent of the burden on the top 1 percent of taxpayers.

Again, there are arguments you could make about whether there are more efficient ways to raise the same revenue from the wealthy or corporations. But one thing is for certain: Wall Street and the Trump administration react with horror at the idea. Treasury Secretary Steven Mnuchin said this week that such a tax “would destroy our capital markets.”

This is at a time when the Trump tax cut pushed profits of the banking industry to a record $237 billion in 2018, and the administration is gutting oversight of Wall Street. Isn’t that an argument Democrats would like to have?

Democrats don’t all agree on every specific proposal, which is fine. But they can all agree that the system has to be reoriented away from the interests of the wealthy and toward the interests of regular people, whether it’s in taxation or regulations or health care or education.

What they don’t do often enough is talk about all those issues in these terms. Some candidates do, but it’s something all of them should do. It doesn’t matter if your tax plan is the one that hits the wealthy the hardest; you can still make an argument about inequality and unfairness in the system.

Again and again in recent history, Democrats have left this incredibly potent set of arguments sitting on the shelf. They put out plans to raise taxes on the wealthy, but they don’t place this critique at the center of their campaigns. They don’t hammer it day in and day out. They allow someone like Trump to claim to be a populist.

And all it takes is someone saying, “Hey, didn’t you get some donations from people who work on Wall Street?” to make them clam up and change the subject.

But this argument is so effective because it resonates with people’s lives and what they see around them. It connects specific policy proposals to broader themes about what’s wrong with the system and how to change it, and whom Democrats and Republicans represent. And most revealingly, it’s the last thing any Republican ever wants to talk about.

That should be all the incentive Democrats need.

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