Establishment Democrats have a plan for 2018: nationally unify around an anti-Trump message and then micro-target policy positions by: district and tightly defined demographic clusters. This is not a stated plan, if you asked them I am sure they would claim to have a positive progressive message, but their strategy is very clear from what they have been doing publicly, and the position papers that have leaked out. This is an incredibly stupid strategy.
It is time for the Democratic establishment to take a firm, national stance on a few public policy positions. Let everyone in America know a core set of priories they will pursue if/when they regain power. These should be policies that are incredibly popular and core to the Democratic Party, as well as popular in the general voting population, and urgently good policy. Democrats have these positions on: healthcare, taxes, and guns.
There are many topics where there is not a clear Democratic consensus on public policy. This includes a lot of foreign policy positions where the Democrats range from nation building to isolation. This also includes trade where the Democrats range from free trade to protectionist. This even includes some more social issues like criminal justice.
There are some topics where there is a clear Democratic position, but it is not very popular with the general voting population (i.e., popularity including: Democrats, Republicans, and independents). This includes many social issues where there is a legitimate divide in the electorate between the Democratic and Republican positions. Depending on the exact policy, this may also include immigration: keep undocumented immigrants already in the country on a path to stay and work is very popular, but allowing more legal immigrants into the country is not.
There are even a few topics where there is a clear Democratic position, but it is not actually that great of policy.
There are three issues where the Democratic position is core, it is generally popular, and it is urgently good policy. There are two obvious ones: healthcare (i.e., ability for anyone to buy Medicare, if they choose) and taxes (i.e., roll-back part of corporate tax cut and use money for social safety net and infrastructure). And one emerging topic, gun safety (i.e., limit magazines to 10 bullets, universal registration of guns and owners, and assault rifle ban).
It seem ridiculous to have to argue why a party should back core policies that are popular with the general population and is urgently good policy, but:
1) Create Trust in Democratic Party by Backing Issues: Democratic voters do not trust their party to do anything, because they are constantly folding on policy positions for the sake of "compromise" and "bipartisanship". The great policy accomplishment of President Obama was passing a right-wing think-tank's healthcare plan for more market solutions. I am happy it passed, because it is much better than what the US had, but it still not ideal for Democrats. The great policy accomplishment of President Clinton was limiting access to the social safety net.
If the Democrats do not back core issues, that are incredibly popular, and urgently good policy: when do they back anything? Reminder: Republicans are fine passing incredibly unpopular and horribly destructive policies, like massive tax cuts for rich and sabotaging the market for health insurance, that are not even popular with their base.
2) Economies of Scale: it is cheaper and more effective to run ONE national policy positions than 435 different policy positions.
3) Republicans will Define Democrats, if they refuse to do so themselves. Republicans are going to argue that the Democrats want mandatory single payer healthcare that forces everyone off of their current plan. Some Democrats do want this, but it is a much less popular position than the option to buy Medicare. Republicans are going to argue that the Democrats want to raise YOUR taxes. This is really unpopular (few people want to raise their own taxes!), while raising the taxes of the rich and corporations is really popular. Republicans are going to argue that the Democrats want to ban all guns, which is also really unpopular, while the serious, but limited, gun safety measures are all generally popular.
Note: some Democratic "strategists" learned the wrong lesson from Republicans' "repeal and replace" of Obamacare: Republicans won by not having a plan, which is great only if your actual plan is evil. Democrats were not able to actually pin on them a plan that was nearly as bad as their actual plan because journalists would refuse to print the crazy notion that the Republicans would just repeal and do nothing. While Republicans will pin on Democrats plans that are much worse than their actual plan.
4) The 2018 election will be a referendum on President Trump, no matter what the Democrats propose, but it relatively cost-less (actually positive) to promote good policy and cast President Trump/Republican policy positions as even more evil than people currently assume they are: when it is fully implemented, the Republican tax plan actually raises taxes on the majority of US households. That looks bad, but it looks even worse when compared with a Democratic plan to keep their taxes down by raising the taxes of high income and corporations. The Republican healthcare plan would double the amount of uninsured, which looks bad, but looks even worse next to a Democratic plan to push uninsured down to zero. The Republican gun safety plan would just add more guns, which is stupid, but looks worse next to Democrats' sensible legislation.
5) Stop Letting Republicans Set Agenda: Republicans win when they lose, because they control the boundaries of the debate. Democrats need the healthcare discussion to move away from tweaks to Obamacare and focus on massive access to government subsidized healthcare plans. Democrats need the tax discussion to move way from how much we give rich people, to how we make the tax structure more progressive. Democrats need the gun safety discussion to move past tweaks to background checks to meaningful overhauls that make gun production and ownership look a lot more like cars.