It is unconstitutional for police officers to be exempted from the laws that are established to govern ALL Americans. All Americans are equal and should be treated as such. If a police officer chooses to use deadly force, and it ends in death, they should be indicted on all applicable charges, and brought to justice before a jury of their peers.
It is the President's obligation to ensure that the laws are being carried out FAITHFULLY, and to protect the civil liberties that so many before us have died fighting to protect.
Should a police officer need a self defense plea, they can make one on the grounds of justifiable homicide, just like every other American.