For small businesses, a president taking power can immediately affect business. Small business owners make decisions based on their expectations of future, colored by their emotional state, so if they believe that a Republican President will be good for business, then they’re more likely to order new machinery, hire an extra person, etc. In an ecosystem of small businesses, that optimism feeds on itself.

Happens in big business, too. S&P500 gained 3+% the day after election, which (if you don’t believe the daily stock market is just gambling) presumably means that ‘the market’ expects 3% more growth out of all those companies, just by Trump’s win being formalized. Stock price up makes it easier for companies to raise capital to expand, buy out competitors, etc

Neither of those things is “the economy,” but they can feel like it, if you’re close enough.