Actually, a President is usually responsible for their part in the economy after being in office about a year, becoming more responsible as time goes on. That allows any policy that they have put in place to have impact. Of course, the impact depends on how bad things had been. Obama inherited a TERRIBLE economy from Bush. Trump has inherited a rising economy from Obama. The current economy is still responding to Obama. If it still rising 6-9 months from now, that's due to Trump.
Obama did some things that were good for the economy.
Judging by the performance of the stock market, the mere anticipation of his departure from office was chief among these.
The terrible economy inherited by Obama was resultant from the actions of Presidents and Congresses dating back many decades. The Glass-Steagall final repeal, as an example, was signed by Bill Clinton.
If the bubble had not burst in 2007-8, it would have burst soon after. That said, there is not a person in the country that did not either contribute to or benefit from the Sub-Prime lending debacle. in this way, EVERYONE in the USA was responsible.
Obama, IMHO, characterized the economy as a pie of fixed or shrinking size and the rich needed to be stripped of their wealth to make the poor better off. A zero sum game means some need to suffer for others to prosper. It also fits into the victim/victor paradigm that Obama was constantly selling.
Removing the reward part of the risk/reward set up leaves only the risk.
Trump, again IMHO, rightly characterizes the economy as an ever growing fountain always accommodating the needs of more people who care to risk their time or treasure or both.
The Stock Markets are a measure of nothing more than hope and confidence.
Trump offered hope of a positive change. The markets' growth and the resulting 4 trillion or so increase in the wealth of the citizenry is a welcome change.
The way to make the economy fly isn't much different than raising children. Carrots and sticks are both useful. Constant use of the stick with no carrots and the kids become afraid to venture.
When ALL actions are punished, how will the right actions be repeated?