Fox News is playing to their audience.
While Fox News should be "fair and balanced," rather than just claim it; they only make money if they keep people watching.
Their audience doesn't like Obama, so they play things that make Obama look bad.
But to be fair, if they want to play one side or the other they should toss the title of "News" and the slogan of "fair and balanced." That's false advertising.
It is an opinion channel. They should be truthful about that. But since when did truthfulness matter in politics?