MICHAEL BARONE: Old political rules of thumb are yielding to even older ones.

One reason old political rules stop working is that one generation of voters has different experiences from those of the generations before. Voters who remembered the Depression and World War II in the 1940s rewarded incumbent presidents who seemed to have produced prosperity and peace with landslide re-elections.

They were willing to cross party lines to express their gratitude for policies that seemed to prevent horrors that were then all too familiar. So incumbent presidents of both parties won between 57 and 61 percent of the popular vote in 1956, 1964, 1972 and 1984. Since 1988, only a shrinking sliver of voters remembers what Americans used to call “the Depression” and “the War,” and no president has won more than 53 percent.

Just as Trump has not been able to raise his job rating to the improving economy, so his political enemies have not been able to lower it significantly. Each new supposedly shocking personal revelation has failed to shock; each eagerly whispered allegation of criminal collusion has failed to disenchant.

It’s apparent now that Trump’s support (the 21st-century Republican core, minus a couple million white college grads, plus a couple million white non-grads) is sticking with him pretty much regardless of events or outcomes. And the coalition that makes up the 21st-century Democrats, with the reverse adjustments, is solidly arrayed against him.

This is actually in line with old political rules, rules with origins going back long before the 1930s and 1940s. The Republican Party, from its formation in 1854, has been built around a core of people considered to be ordinary Americans, but not by themselves a majority. The Democratic Party, from its formation in 1832, has been a coalition of those regarded as out-peoples, often at odds with each other, but together often a majority.

Both parties’ voters today are acting in characteristic fashion. The vast body of Republicans has no truck with the complaints of Never Trumpers. The Democrats are in turmoil, panicking at the possibility of having enemies on the Left, to the point that House Democrats couldn’t pass a resolution decrying the blatant anti-Semitism of one of their own.

Well, it’s hard to decry blatant anti-semitism when a major constituency of yours consists of blatant anti-semites.