Members of Congress are afraid to go after Obama because of a combination of these two factors:
1. The media would label them as racist since Obama looks black.
2. Congress is complicit in the biggest hoax/fraud (Obama presidential usurpation) in US history.
If Congress goes after Obama, the truth emerges and many of them go straight to prison for treason.
Racism fear is a significant factor, but the main reason they will not act is that Members of Congress are protecting Obama to protect themselves.
It is that simple.