Walter Mondale's complaints about President Reagan remind me of the grousing I used to hear as a boy in Louisiana about the Long family's political dynasty. This was many years after the fact in the case of Huey, and shortly after in the case of Earl, but the wounds were still fresh: That man, I would be told, was a demagogue. He said wild things and never got called to account for them.

The pure frustration that emanates from Mondale on the subject of Reagan and taxes, or Reagan and the deficit, or Reagan and the Russians, is of the same kind. The sheer effrontery, the gall, that, for example, blaming the size of the deficits on the Democrats requires is staggering -- yet Reagan gets away with it.

The standard explanation as to why and how is that although people disagree with Reagan's policies, they like him personally, and that overrides the disagreements. But that doesn't really capture the dynamic of the relationship between Reagan and his constituency.

Talk to people who are going to vote for Reagan -- not professional politicians and handlers, but people for whom politics is not at the center of life -- and what you'll hear over and over is that, okay, he's not perfect, but he's basically on the right side. Sure, he might raise taxes, but if he does it, it'll mean taxes really need to go up; Mondale likes taxes. Sure, his new conciliatory mood about relations with the Soviets seems to be a reversal of field; but if Reagan feels it's safe to negotiate, it must really be safe.

In the case of Huey Long, it was an explicit part of his message that he was going to govern in a way that would look out for interests of one kind of person -- the little man. If his explicit positions were often irresponsible that they didn't stand up to close analysis or further the tenets of good government, well, that was quibbling. The main point did not lie in such details; it was to lift the little man up and teach the big man a lesson.

What is officially called demagogy by politicians is often really a way of sending this kind of signal -- of saying: What I want you to remember about me is not my specific positions but that I'm going to help my people. Thus in this year's Democratic primaries, the most "irresponsible" candidate, Jesse Jackson, was also the only one who really saw himself as the leader of a clearly defined constituency.

Long and Jackson, like most politicians of the genre, stood at the head of a vast stirred- up army of the dispossessed. What's unusual about Reagan is that he sets himself up in the same way, but attracts a very different kind of following -- a vast stirred-up army of the possessed, if you will. When he says that Waltr Mondale wants every day to be April 15 and Ronald Reagan wants every day to be the Fourth of July, it's hard to believe you're listening to a sitting president, it's such a pure statement of us-and-them, and so unhesitant about the use of poetic license.

Who are Reagan's people, and who do they think is their enemy? They can't be just "the rich," because there aren't enough of them to give Reagan as big a lead as he has, though certainly he'll do far better above the median income than below it. More precisely, they're people who feel that the many ententes by which America has been governed since World War II -- from the welfare state to establishment foreign policy -- have left them net losers. I may not be hurting economically, the feeling goes, but the last generation's worth of arrangements that have been made in Washington and New York must be helping somebody else a lot more than they're helping me.

Reagan knows how to, as the ad men say, connect up with this feeling. When he talks about the bright future, it's a way of saying that these arrangements won't exist any more. Though rhetorically he's the most anti-establishment president in years (except perhaps Jimmy Carter for about a year), he's obviously the postwar president most personally indifferent to the establishment's approval. You can't imagine him brooding in the White House of an evening, like Lyndon Johnson or Richard Nixon, because they're laughing at him at the Harvard Faculty Club. His very success proves how little that matters any more.

The purest us-and-them American politicians usually lose. When they get to run a government, as Huey Long did and Reagan has, it's worth remembering that they remain true to their emotional message. After they're gone, what seems important about them is not this or that policy, but that they delivered for their people -- and that in the process, power in the society changed hands, having been taken from its former holders and given to the people who put the head man in office.