The Post's graphics team has a great new tool allowing you to compare turnout between presidential election and midterm elections among a whole bunch of different demographics.

We encourage you to play with it here, and below we'll offer a few observations.

This chart, better than just about anything, shows Democrats midterm problem -- specifically how their party base, while good for presidential elections, isn't exactly conducive to winning the non-presidential elections in-between.

Let's compare the midterm drop-off among the key parts of the so-called "Obama coalition" to more GOP-friendly groups.

Young people (who President Obama won by 23 points)...

... compared to senior citizens (who went for Mitt Romney by 12 points).

Now, switching to race, here are African Americans (who are almost exclusively Democratic voters)...

... compared to white voters (Romney +20).

And, lastly, here's another key portion of the so-called "Obama coalition" -- unmarried women (Obama +36)...

... compared to the inverse (and Romney +22), married men.

The differences in some of these cases (particularly race) are slight, but they are real and consistent. And in tight elections that are decided by a few points, a couple points in turnout difference in a key demographic or two can make the difference between winning and losing.

This is Democrats' big challenge come Nov. 4.