If you think about the most salient or well covered things by the news in each of their presidencies, they're right there in the header. I'd say it's difficult to write in an unbiased sense about these issues, and given the difficulty, Wikipedia has done a decent job.

What exactly do you see as a "negative portrayal"?

And disagreeing with the supposed "negative portrayal" or disapproving/approving of the actions of one does not make an article biased.