Just find tight senatorial races and contribute to the D. Maximum impact will be to wait until after the primaries, though. The DSCC usually has this information available (though don’t contribute to the DSCC, nor to the DCCC). I say “Senate” and not “House”, because that’s where we need the big win this year.
Tight races often involve a conservative Democrat, so you will need to be able to not worry about their ideology.
I usually “adopt” a district, Senate or House, outside my area and contribute strongly to a single candidate. For example, in 2005 Melissa Bean, a pretty conservative Democrat, had a slim chance to beat Phil Crane in the Illinois 8th. Crane was one of the worst people ever in the GOP, even by today’s standards; back in the 70s I had actively worked for a candidate against him in the 13th district. I didn’t like Bean, and had I lived in the district I would probably have supported one of her opponents in the primary, but thanks to contributions from individual donors like me the DCCC finally decided to risk some national money on her (despite the 8th being a “safe” R seat), and she won.
Incidentally, the 8th has been held by Democrats for all but 2 years since then, including by the person who coined the nickname “corporal bone spurs”.
