KEVIN LAMARQUE/REUTERS – President Obama shakes hands at Sloopy’s diner inside the student union of the Ohio State University in Columbus, Ohio, on August 21, 2012.

Harvard’s Institute of Politics has released one of its regular polls of millennials.  It’s been making news mainly because it suggests that young people are not enthusiastic about voting in the upcoming midterm — which, if it turns out to be true, does not bode well for Democrats.

But there is another problem lurking for Democrats: the youngest millennials are not actually that Democratic.  In fact, they are barely more Democratic than Republican.  I have pointed this out before, using a different set of polls.  The Harvard poll suggests the same thing.

Below is the party identification of millennials broken down by age group.  (I thank Esten Perez and John Della Volpe of Harvard for providing me these data.)

The graph captures the percent who identify with or lean toward the Democratic or Republican parties.  The remainder identify as independents and do not lean toward either party.  Older groups of millennials are decidedly Democrats.  For example, the Democratic advantage is +18 (48%-30%) among 27-29-year-olds.

But among younger millennials, that advantage shrinks.  In fact, Democrats and Republicans are essentially tied among 18-20 year olds: 41 percent Democratic and 38 percent Republican.

As I noted in my first post — and as Dan Hopkins recently described in more detail — the explanation is straightforward: the partisan complexion of each new generation reflects underlying economic and political fundamentals, like how well the economy is doing and how popular the president is.

Thus, it’s hardly any surprise that the youngest millennials are not as Democratic as older millennials. The youngest millennials came of age politically under a Democratic president whose popularity is below average and who has presided over a sluggish economy.  Older millennials came of age politically under a Republican incumbent who became even less popular while presiding over a controversial war and a catastrophic recession.  There is no reason that the two groups should be political twins.

Of course, the political formation of younger millennials isn’t over.  Their attitudes may evolve throughout young adulthood, and perhaps in a direction benefiting Democrats.  But the early evidence suggests a potentially significant challenge for Democrats: the newest voters aren’t that Democratic after all.