That's because that has been the pattern when a new president from a different party takes office, said Tom McClellan, editor of the McClellan Market Report.
After the election, hopefulness and euphoria usually sends stocks higher because "everybody assumes that whatever's wrong is going to get changed or fixed by the new guy even though nobody's doing anything yet in terms of governing," he said in an interview with "Closing Bell" on Tuesday.
However, the morning after the inauguration, people realize the problems still exist and it will take longer to fix them, he noted.
"That tends to bum everyone out and so they sell their stocks."
And that's not the only thing that can discourage investors, according to McClellan.
Typically, a new president from a different party finds that things are worse than he said during the campaign, and the only solution is whatever package of tax cuts or tax hikes or spending he wants to get through Congress, McClellan explained.
"Investors don't like to hearing that things are worse than we expected and that tends to depress prices during the first year of a new term."
Trump will be sworn in as the 45th president of the United States on Jan. 20.