I'll avoid the obvious political cheap shots and comment on the golf aspect of the story only. 
Harmon doesn't really need the any more big names to add to his client list or press coverage but he can't pass up an opportunity to work with the POTUS. Not only is it an honor to be asked by the POTUS, the media backlash from refusing would be too damaging, just look at the heat Phil took for complaining about his taxes. Butch can write off the expenses, I'm sure this will provide him some extra deductions and good will from the IRS.