1. Distract from caravan news coverage, especially now that people have found out about the MS-13, ISIS, Middle Eastern and other non-poor Honduran participants riding on the back of trucks.
2. Distract from the bad election news that even the Dems' own news media are predicting no blue wave whatsoever.
3. Try to drum up sympathy, in light of news described in 2., above, i.e., "vote for us because the big, bad GOP is sending bombs."
4. Reichstag Fire: blame a white, Christian, southern, Republican, Trump-supporting, conservative (any of the foregoing adjectives) male for the "bombings" to justify a like response.
I'm sure there are a lot of reasons that make sense to a Dem why they should fake being the victims of terrorist bombings.