Let's see:
cult –noun
1. a particular system of religious worship, esp. with reference to its rites and ceremonies.
Nope, not a religion or religious in nature.
2. an instance of great veneration of a person, ideal, or thing, esp. as manifested by a body of admirers: the physical fitness cult.
It may fit this definition. But so would the Democratic party.
3. the object of such devotion.
As above.
4. a group or sect bound together by veneration of the same thing, person, ideal, etc.
As above
5. Sociology. a group having a sacred ideology and a set of rites centering around their sacred symbols.
Nope. No rites, no sacred ideology.
6. a religion or sect considered to be false, unorthodox, or extremist, with members often living outside of conventional society under the direction of a charismatic leader.
Again, not a religion.
7. the members of such a religion or sect.
As above.
8. any system for treating human sickness that originated by a person usually claiming to have sole insight into the nature of disease, and that employs methods regarded as unorthodox or unscientific.
Nope, not a panacea sales machine either.
So, I think a political party, no matter what its most extreme members are up to, would qualify as a cult unless it stopped being a political party first.