It's interesting that the Russians don't appear to be targeting Democrat as vigorously. I've seen some bits of Russian disinformation targeted at progressives (often, trying to drive a wedge between far-left and centrist Democrats), but they don't seem to be devoting the same effort.
I don't believe that Democrats are less resistant to disinformation. They haven't got the save level of infrastructure devoted to it, but I feel like the Russians could spin it up themselves if they wanted to.
I wonder if it's a conscious decision: Republicans seem willing to believe all kinds of false things about Democrats, and it would be unnecessary to actually make the Democrats believe additional false things. Or maybe they like the way Democrats sputter at their inability to get past the Republican-targeted disinformation.