Is It Fair to Smear a President While He is Still in Office?

If the POTUS is the most powerful man in the world, should we be smearing him while he's still in office? He is an elected official (as in people voted him there) and we all know that he will be in office for atleast 4 years. So, why smear him while he's still running things? It's not like it will get him out of office faster or that the people can rise up and overthrow him. What's the point? Can't wait til he's out of office to ruin his legacy?