Why does it matter if Obama was accepted at Harvard on Affirmative Action?

From what I have heard Trump has said something along the lines that Obama got into Harvard with not so stellar grades. I guess he is implying Obama got in due to affirmative action? Is that it? Or, is he saying Obama was accepted to Harvard by some sort of connection not on the up and up?

It seems Obama did very well at Harvard, and was President of the Harvard Law Review. Obviously he applied himself well while studying at Harvard.

What I don’t get is on TV they keep talking about high school grades, but wouldn’t his college grades, undergrad, be what is important? Who cares how well he did in high school.