The fifties, sixties, and early seventies were years of sky high top bracket income taxes, strong economic growth, and rapid improvement in median American incomes. They were also the last years of Democratic Party political dominance. Sometime between then and now, the Democrats lost the confidence of the American working class, especially working class men. How so?
Well, of course, it's complicated. Wars, race, oil shocks, terrorism all played their parts.
Political parties tend to be dominated by elites. The great depression and it's economic questions, and the struggle against Fascism and Communism had dominated the Democratic Party and its elites for a generation, but by the sixties and seventies social issues had come to the fore. Social issues have dominated the mind of the party elite every since: civil rights, feminism, abortion, immigration, gay rights. Enormous progress has been made on many of these issues, in the law and in public opinion, but these wars were never the wars of many white working men, and some have threatened them very directly.
Meanwhile, the Democratic party supped at the tables of the Wall Street and corporate lobbyist fat cats, and the position of the American worker has steadily deteriorated. Of course a lot of that deterioration is a direct result of the Reagan and Bush tax breaks for zillionaires policies, but voters have plenty of reason to be unhappy with the flabby defense provided by the Democrats too.