Business and investment are gonna mostly happen as usual.
Except they're not.
On the business side, every survey of business leaders as well as every other indicator of capital investment shows that they're hunkering down: deferring or even cancelling any plans to expand, freezing hiring (if not actively working to reduce staff), etc. Good businesspeople can deal with almost any economic and regulatory climate you throw at them, but the one thing they need is predictability. Business is all about planning, and you can't make plans in the fact of chaos.
On the investment side, yeah, Wall Street seems surprisingly optimistic, but if you look at bond markets you see a different story. The most concerning part of it is that normally money floats back and forth between stocks and bonds, depending on the economic conditions. When stocks fall, the money flows into bonds and their prices rise (causing their yields to fall -- which is good when the government needs to borrow, which is always). When stocks rise, the money flows out of bonds and back into stocks. But this isn't happening so much right now. Equity and bond prices are falling together (and bond aren't recovering when stocks do).
How can that happen? It can happen when capital is fleeing the country. Investors are pulling their money out of the US, equities and bonds both, likely sending it overseas.
On the other hand, main street is getting lightly hammered.
Indeed.
Trump will finish out his 4 years. Looking back, we will realize that he accomplished and changed surprisingly little.
Unless he keels over soon and Vance proves to be more rational, I doubt it. Actually, I think you're overly optimistic even if that happens today, and even if Vance proves to be an outstanding president.
Trump has already irreparably damaged our economic and military alliances around the world. The world was sort of okay with trusting us again after Trump lost in 2020, but November 2024 proved that America is no longer a trustworthy ally or trade partner. The world's alliances and trade networks are treating us as damage and working to route around us.
DOGE has significantly gutted many US agencies, and it's going to take a very long time to rebuild that lost state capacity. We haven't yet seen the impacts of that foolishness yet, in part because state capacity was already pretty low (on a per capita basis, the federal government had reached a nearly century low), but we will.
Trump's budgetary plans will add $6T+ to the debt, at the same time he's pushing up bond yields, making it more expensive to finance the debt.
I'm slightly more optimistic that we can reverse Trump's kleptocratic moves. SCOTUS has made sure we'll never be able to hold him or any future president accountable for taking massive bribes, but maybe we can keep the rest of the government from following suit. It's not a given by any means, though.
Finally, Trump's actions on immigration and science funding are already causing likely-irreversible damage to our research base. US researchers are applying overseas and foreign researchers are not applying to come to the US. Long-term studies have been shut down. For example, I saw that a large-scale (~190k participants) long-term (~40 years so far) longitudinal study of breast cancer has been shut down. If funding is restored quickly, that can be restarted. If it isn't restored until 2029, there will be a significant gap in the data. But that one at least can probably be restarted. In other cases researchers or facilities may well be gone.
The US' post-WWII global dominance was built on two primary foundations: Technological progress and trade, with foreign aid playing a significant supporting role. Trump has done an incredible amount of damage to all three in just four months in office, enough that we won't recover quickly, and will never recover all of what we've lost. If he gets to continue thrashing about for four years, it's gonna be pretty bad.