The second group is the upper middle class — roughly the 90th to 99th percentiles of earners — whose pay increases have essentially kept pace with economic growth: Not great, but not bad.

The final group is the bottom 90 percent, whose raises have trailed G.D.P. growth. Their share of the economic pie has been shrinking.

The trouble with Obama’s tax policy (which Hillary Clinton and Bernie Sanders mimicked in the 2016 campaign) was that it didn’t distinguish between the second and third groups. It promised a tax cut to the poor, the middle class and to the upper middle class.

There was good political reason for Obama to do so. It allowed him to avoid divisive debates about who was truly rich. In the group of nonrich, he included a lot of affluent professionals who also happen to play an influential role in the public debate — journalists at national publications, prominent economists, think-tank experts and others. Many of these people earn six-figure salaries while thinking of themselves as middle class.

But Obama’s approach means that the federal government has ended up being overly generous to these upper-middle-class households. In my column, I praised the 2020 Democratic presidential candidates for focusing their tax proposals more on the poor and true middle class. That’s even more important now than in 2008, because of the financial crisis and its aftermath.

In his Facebook post, Obama was careful to note that he did not agree with “every single thing” in the articles he was recommending. And I don’t claim to know exactly what he thinks about tax policy. But I think it would be perfectly reasonable for someone to believe that Obama’s tax plan was right for 2008 and not quite right for 2020.

Obama’s other suggestions

“White Nationalism’s Deep American Roots,” by Adam Serwer in The Atlantic.

“Keep It Simple and Take Credit” (about the political importance of simple government programs), by Jack Meserve in the journal Democracy.