How to explain this? The Republican National Committee is outraising the Democratic National Committee among small contributors (those giving $200 or less), by $40 million to $25 million so far this year, according to a Saturday front page story by the Washington Post's Matea Gold. And that's not primarily because special interests are seeking influence with the party in power.

It's small contributors, those giving $200 or less, who donated $239 million to the Trump campaign in the 2016 cycle, more than to Hillary Clinton's and Bernie Sanders's campaigns combined.

Similarly, in the most important statewide election this year, for governor of Virginia, just 8 percent of Democrat Ralph Northam's donations are from outside Virginia, compared to 35 percent for Democratic Governor Terry McAuliffe in 2013, according to the Daily Beast's Sam Stein.

This is at odds with polling showing Democrats more engaged in politics and more interested in voting, and also with the large number of Democrats running for Republican-held congressional seats. I can think of specific reasons why small donor giving to the DNC and to the Northam campaign is so tepid: The DNC leadership team — especially DNC Deputy Chairman Rep. Keith Ellison — has a record on some issues must surely be offputting to many Jewish and pro-Israel donors, and Virginia's state campaign finance rules allow Northam to raise so much money in large contributions from Virginia special interests that he doesn't have much need of small contributors.

In addition, Democratic small donors in the nation pitched in heavily for Democrat Jon Ossoff in Georgia's 6th Congressional District special election in June, helping make it the most expensive House race in history. Some 86 percent of Ossoff's money came from outside Georgia, much of it in small contributions.

What explains the difference? I think the Cook Political Report's Amy Walter has a valuable clue when she reports that Democratic enthusiasm, like the Democratic electorate, is geographically and demographically clustered. Walter cites CNN polling that shows 44 percent of Democrats but only 34 percent of Republicans saying they are extremely or very interested in voting for Congress, a 10 point enthusiasm gap. This contrasts with Republicans' 20 point advantage in the enthusiasm gap going into the 2010 congressional election, in which they gained 63 House seats. But the Democrats' advantage seems concentrated in the 194 Democrat-held congressional districts.

Walter cites NBC/Wall Street Journal polling showing Democrats 29 points ahead of Republicans on the generic ballot question (which party's candidates will you vote for for Congress?) among voters in the seats held by Democrats. That's twice the Republicans' 14 point advantage in the 241 Republican-held seats. That 14 points is comparable to Republicans' advantage in Republican-held seats in 2010 (15 percent) and 2014 (18 percent). "In other words," Walter writes, "it look as if Democrats may ‘waste' their enthusiasm advantage in districts they already hold."

That seems in line with my sense that lots of Democratic candidates are running — maybe so many as to create troublesome primaries — in high-education districts, which include most of the 23 Republican-held seats that voted for Hillary Clinton over Donald Trump, and also Georgia 6, which has the sixth-highest percentage of college graduates of any district and gave just a thin plurality of its votes to Donald Trump.

If this analysis is correct, Democrats' chances of winning a House majority depend on somehow extending the anti-Trump enthusiasm beyond the cocoon — beyond the central cities, sympathetic suburbs and university towns where Democratic voters are increasingly clustered. So far, it's not clear that they can do that.

Footnote: The redistricting case brought by Wisconsin Democrats, currently before the Supreme Court (which I wrote about in a recent Washington Examiner column), is an attempt to require that congressional and legislative districts be drawn to do just that: by requiring geographic tentacles extending outward from heavily Democratic areas to include some, but not too much, Republican-leaning territory, much like Illinois and Maryland Democrats' current congressional district gerrymanders.