Sure they can, if they're the same three million people who lost an election.
Trump already knows millions of people voted against him. Those same people making a big stink about how they exist and don't like him isn't going to change anything.
If these millions of protesters were instead millions of get out the vote volunteers in September of last year, they might have made a difference when making a difference actually mattered to the outcome. These millions reminding us of their existence now is redundant and useless.