If the Dems get up, the one thing you can bet on is a return to normalcy. Sensible fiscal policy! Less dysfunction in Washington! Oh man it would be fantastic.
A few other random bits, possibly with some angles available to speculators and investors:
1. Democrats favor national marijuana decriminalization, and consequently the volatile cannabis industry could do better.
2. Somewhat relatedly, treatment centers for addiction should also do better and private prison operators and prison-related goods and services worse. Democrats want to shift from prison as a common response to simple illegal drug possession to treatment centers and services as the dominant response.
3. There could be some impacts in the healthcare and pharmaceutical industries, but probably this'll only bring forward trends that are already baked in. It's very, very tough now for healthcare spending to grow much beyond its current outsized fraction of U.S. GDP, so something has got to give.
4. There should be some stepped up antitrust enforcement, particularly in the technology sector. It wouldn't surprise me to see one or a couple mega market capitalization companies broken up over the next few years, and that could be a very good thing for investors.
5. Green technologies should do well, and the fossil fuel industry could lose its subsidies. I've seen some reasonable arguments that companies like Tesla could benefit, perhaps justifying (or coming closer to justifying) its already lofty valuation.
6. Relatedly, there should be a significant boost to infrastructure spending, particularly for repair and rehabilitation. Things like adding insulation to schools, government buildings, and homes. Switching street lighting to more energy efficient lamps. Adding sidewalks, bicycle paths, and traffic "calming" features. Planting trees and restoring wetlands. Smart traffic management systems. Mass transit and Amtrak, the national passenger rail system. (Joe Biden is probably Amtrak's most famous regular customer.) Fixing bridges, municipal water and sanitation systems, and electric grids. Environmental cleanup such as capping oil and gas wells that are leaking methane. Etc., etc.
7. Retirement savings plans such as 401(k)s and 403(b)s would change somewhat in terms of how the U.S. government gives them tax preferences. Currently retirement savers in the highest tax bracket get the most benefit. Savers in a zero or negative tax bracket get no benefit (or even negative benefit), although Roth (after-tax) plan variants can still sometimes work, and employer matching funds if offered are still beneficial. The Democratic proposal is to flatten the tax advantages so that everyone participating gets some benefit, skewing the benefits more toward lower and middle income earners (or unskewing them, really). I've seen some ridiculous reporting that this might cause angry CEOs to cancel 401(k)s completely because they aren't getting enough benefit personally, but no, that's not going to happen. For one thing, CEOs and other highly compensated individuals still get a tax break. It's just a smaller one, that's all. They're not toddlers, not often anyway. Also, even if a few act like toddlers, other employers would just snap up those workers by continuing to offer 401(k)s or even making them more attractive. Less than half of U.S. workers have 401(k) plans today, so what I think is much more likely to happen is that some greater percentage of workers will participate, by a few percentage points anyway.