Many of the possible focuses of the upcoming Congressional Elections appears to be topics that are predictably partisan. Voters have already taken positions on most of the issues. The one issue that stands out as being a possible game changer is corruption in the Trump administration. Voters are almost always willing to put agendas aside when it comes to acknowledging and admitting even a favored politician is ripping off the treasury and taxpayers. American voters have shown acceptance for bad behavior as long as it does not include financial corruption. Proven crooks do not do well. The tip of the iceberg is beginning to show in the Trump family to include Trump himself.
If the Democrats fuel their Blue Wave with exposes on Trump family and administration corruption, a Tsunami is on the way.
This is a perfect microcosm for that the Democrats have these mid-terms: nothing but Trump. Any message they've had that speaks to the economy, immigration, abortion, etc... if it's even there, it's taken a back of the bus seat to their screaming about Trump loudly and daily. That's plenty effective for the base who's existences further depend on a steady diet of Trump hate, but for independent voters who are looking for some solutions to their problems... attacking the guy who's lived up to many of his 2016 campaign promises, most namely the economy doing very well, isn't going to cut it. The democrats constant and un-ending complaining about Trump means that they need something truly earth-shattering to get anyone to really take them seriously when they say Trump is such a clear and present danger that needs to be removed from office.
I'm not a Trump fan, but that's just reality for you.