It is not in any way courageous for celebrities to join the herd in speaking out against Trump. It raises their profile and makes them $. And just focussing on Trump, as though the current turmoil started with this one idiot, is not helpful at all. In fact I reckon it has the opposite of it's desired effect, as there will be more Trumps in the future if we keep avoiding critiquing the root causes of his popularity. By defending Obama, war monger McCain, etc, Eminem is encouraging this avoidance.
Speaking out about these root causes; against Obama/Clinton/neoliberalism/militarism/imperialism etc - THIS requires courage.
Here's a great rap response to Eminem