It primarily depends on who is funding the politician's venture within the mall. If it's the taxpayers then that removal would constitute a First Amendment viol

It primarily depends on who is funding the politician's venture within the mall. If it's the taxpayers then that removal would constitute a First Amendment violation even without direction of the government itself. Which is why your local reps office isn't inside a mall, because the mall wouldn't want the unblockable distraction of protesters or public events.