I am on Et Tumor Brute? and I am still only accepted, the next quest is assassinating the president and then the end I have to get liked before the battle for Hoover Damn, any one have suggestions or alternative ways to do this?

Well, completing the quests besides going to the Dam will get you some good points. Also, sell some NCR Dogtags to Aurelius of Phoenix at Cottonwood Cove. Try completing Cold, Cold heart and Finger of Suspicion.

Profligate dogtags are the easiest way.