It is controversial because the President can pardon anyone! Take Nixon and Goldwater for example. Nixon was convicted of spying on th opposite party. Nixon stepped down, but was still charged. When Goldwater became president, he pardoned Nixon of all of his charges which caused a huge uproar. That's fair, right?
What they have in common is that both actions require consent of the senate. The senate has to vote with a majority for those things to come into effect Hope this helps!
