As of last night we have 50-60 democratic Congressmen saying they will not attend the inauguration tomorrow. Trump is going to see this as a slight or even a slap in the face. And Trump is president for the next four years, maybe more. And to get anything to happen in the US of A, the president has to get behind it. At least to speak well of it on TV.
These 50-60 democrats must have things they want to get done. They are all serving for another two years, and they have decided to start off by irritating Trump. Which is going to make it harder for them to get Trump to do anything, OK anything, say nice things about something they care about, appoint their friends to federal office.
The job of a politician is to cut a deal between opposing sides. Part of cutting a deal is not insulting one side. These Congressmen seem to have forgotten that, they are doing insults before Trump is even inaugurated. Good luck getting Trump to help you out on anything, even just renaming a Post Office in your district.
We shall see. Maybe in two years a lot of these guys will be replaced with Republicans.