Were you to look solely at the ideology of the Democrats coming out to vote in the party's presidential contests so far, you'd have to think that Bernie Sanders would be cleaning up. In the three states that have held primaries and caucuses so far, the number of voters identifying themselves as "liberal" is consistently higher than the last contested race eight years ago.

It's a Sanders electorate -- but he's lost two out of three.

We've noted previously that Sanders's party is more likely to refer to itself as liberal than it used to be, according to polling from Gallup. The Democrats still have more space under their umbrella for moderates, but they're getting crowded out.

The Republicans, on the other hand, have been consistently and heavily conservative for some time.

We can see a similar dynamic at play in the ideology of voters in the early voting states. Comparing the three most recent Democratic fights and the three most recent Republican ones, you can see the gradual shift to the left by the Democrats clearly.

That Democrats identify themselves as moving to the left across the board may help explain why Hillary Clinton is running further to the left than she did in 2008 -- which helps explain why she's been successful. (No data for Nevada in 2004 was available.)

The Republican side is different. The electorates in Iowa, New Hampshire and Nevada look different from one another in many ways, but notice that "very conservative" voters have been a smaller part of the electorate than in past years.

Notice too that the surge in moderate voters that gave Mitt Romney an easy victory in New Hampshire in 2012 has receded. Part of the turnout make-up, it seems, is who is running. Donald Trump is less conservative than many in his party, and he's winning with a less conservative electorate.

The question is the extent to which this will be a long-term trend. Will the Democrats keep moving left, further polarizing the electorate? Or could a moderate candidate do well on other side and reshape who turns out?

We'll let you know in four years.