"...who is an atheist, than would younger, less conservative...."

Not necessarily. There are lots of conservative young people on campuses today and elsewhere. And according to Pew, many unaffiliated young people turn conservative when older. "Younger" is not synonymous with "more open."

"...between Christianity and 2 party...."

In the US, the candidate with the most votes is winner of the Congressional seat. The losing party or parties win no representation at all. The unique unity of the Amer. people and the homogeneity of Christianity mitigate against large dissenting groups. But as Christianity shrinks (70% of the population now) and the unaffiliated rise, it is possible that large dissenting groups (say, of conservative Christians [both Protestant and Catholic] or of the unaffiliated) could surface.  So far, however, our two party system has been able to absorb all groups, all religious and non-religious persuasions. This is not the case in Canada, most of Western Europe, etc