A president is not exempted from any crimes he committed prior to taking office. He can be prosecuted. If the crimes occur during his term in office, then he can be impeached.
Were you around in the late 90s? We had a president named Bill Clinton who committed any number of crimes in office and before. Do you know how many crimes he was convicted of? None. Do you know whether he was removed from office? No. Did his party suffer in a major way for it? NO. Do I like that? No. But, at the end of the day, that was the reality. Obama could be guilty of a million crimes. Unless he is prosecuted for it, or the public turns on him, it sadly makes very little difference. Right now, the public is unhappy about his job performance, but they don’t care about his scandals. Is your objective to be “right” and Obama advance his agenda, or turn back his agenda?