Back during the brief period when Democrats controlled 60 seats in the Senate, they could have rammed through a bill to grant statehood to Washington DC. This would have guaranteed them two extra Democratic senators and at least one extra Democratic House member. So why didn't they do it? Jonathan Bernstein suggests that it demonstrates a core difference between the parties:
I think perhaps the reason is that for whatever reason, in recent years Republicans have tended to use their best legislative and executive chances to secure long-term electoral advantages, while Democrats have tended to use theirs to enact substantive policy.....The point here isn't that the Democrats are especially spineless (or that Republicans are especially ruthless) — it's that they (may) think about, and use, power differently.
....Speaking of which...this also explains another of this blog's hobbyhorses, the GOP certainty that Democrats are going to re-instate the Fairness Doctrine in order to shut down Rush Limbaugh and other conservative radio hosts. If it's true that conservatives do think as Drum and I have speculated, then their belief is explained because they know that that's what they would do if they were in a similar situation. And guess what? As soon as they gained a majority in the House (at least this time around), conservatives moved quickly to defund NPR, which they see as the liberal alternative to conservative talk radio.
This is, more or less, an answer to my question about longtime Republican efforts to defund the left: the reason that Democrats don't do the same thing is because they're more interested in passing substantive policy, and there's only so much bandwidth available to them. If you spend all your time on policy, you just don't have time to do a lot of other stuff.
I'm not sure I buy this entirely, since defunding activities are often pursued by different actors than policy activities. Still, it's an interesting notion, and one that jibes with something I've heard repeatedly on the funding side as well: conservative donors are generally eager to fund overtly political activities, while liberal funders are more interested in funding things they consider worthy endeavors. (And more likely to want lots of control over and accountability from the things they fund.) Food for thought.