My questions is different from this post.
Suppose a math's PhD is
1) not very successful in his PhD program research and fails to find an ideal postdoc.(But he is still eligible to gain a PhD degree) or,
2) not very successful in his research as a postdoc and fails to find a tenure-track position like an assistant professor.
and he chooses to be a lecturer for a couple of years just to get rid of the heavy pressure of publishing papers but he is still ambitious about becoming a mathematician. My question is, is it extremely difficult for a teaching-oriented lecturer to get a tenure-track position in mathematics(assistant professor at least)?
BTW, the only example I know about this is Yitang Zhang, whose experience was so special. But in general, I don't know any other examples of a lecturer becoming an assistant/associate professor in U.S.