I want to influence legislation, lobby or assist a certain political candidate. Can I be a 501(c)(3) tax exempt organization?
501(c)(3)s are prohibited from any type of political activity, unless it is to a slight, incidental extent. Even then, the activity is closely regulated. If you want to be a political organization, you can register for a 501(c)(4) organization, which covers social and welfare groups.
An example of a political organization is www.moveon.org. You may apply for tax exempt status under section 501(c)(4). However, donations are still not tax deductible for donors.