In politics, there are no final victories and no lessons that are learned for good: error, like hope, springs eternal. Moreover, what counts as error for some may be wisdom, or at least temporary advantage, for others. There is no catastrophe, political or economic, from which someone does not benefit.
In modern democracies, promises to tax-and-spend are like sin, a permanent temptation: only that they are worse, in so far as they are an instrument for some to gain and (as they hope) to keep power. And so the pendulum swings, seemingly for ever, between extravagance and retrenchment, the former always being more popular than the latter.
In Britain, Mrs. May has overthrown the legacy of Mrs. Thatcher, though nominally she is of the same political party.