Bad news keeps on coming for the Republican Party. This time it’s a detailed survey from US pollster Gallup on party identification, which shows that its in deep trouble among young people (other polls have shown similar results). Republican identification is reasonably stable, between 26% and 34% in most age groups, but plunges as low as 18% among the under-30s.

Plotting the difference between Democrat and Republican identification, as Gallup does, shows an interesting pattern. The Republicans do better, as you might expect, with seniors, but also with Generation X, now in their 30s and 40s. Democrat strength is not just among the young (Gen Y), but has a secondary peak with those in their 50s — the baby boomers.

People often talk as if cohort voting is just a matter of age: that is, if 60-year olds are now voting conservative, in 20 years time 60-year olds will still vote conservative, even though they’ll be a completely different group. But there’s more to it than that; the evidence suggests that the formative experiences of people’s youth continue to affect their political views throughout their lives.

Nate Silver at fivethirtyeight.com graphs Gallup’s results on the basis of “who was President when you turned 18?”, with interesting results. That’s unlikely to be the whole story, however, because the pattern repeats itself outside of America.

Look at the data, for example, from the French presidential election two years ago. As I reported at the time, the centre-right’s Nicolas Sarkozy received his strongest support not just from the over-60s, but also from Gen-X; the opposition Socialists were heavily favored by the boomers as well as the young.

And in Australia we had the controversy over the supposed youth vote for John Howard, exposed by Peter Brent and others as a myth. Ian Watson, writing for Australian Policy Online, concluded that “as the ‘baby boomers’ age, the voting patterns of older Australians appear to be changing in a direction which is adverse for the Liberal/National Party vote.”

None of this should really be surprising. The voting behavior of the boomers, who mostly came of age in the late 60s and early 70s, can be interpreted in one word: Vietnam. The case of Gen-X isn’t quite so simple, but they came of age during the era of Margaret Thatcher and Ronald Reagan, when the left was in retreat worldwide.

As I put in in 2007, “You may care about who will give more money to nursing homes, but it also matters whether the war of your adolescence was Korea or Vietnam (or Grenada, if you’re Gen X).”

So if the crimes of George W Bush and the rise of Barack Obama have tilted the most recent generation firmly to the left, that may have electoral repercussions for many years to come.