This is kind of related to my previous question that was poorly stated because of misreading my own notes that I have taken on the papers I am currently reading, so no surprise that it eventually amounted to something trivial in prime number theory. (I am also surprised that it got upvoted so much!) I apologize for my clumsiness!
The real question that I had noted down and was meant to be asked is the following:
Let $\chi$ be a primitive character $\pmod k$. Then by Pólya's inequality we have $\forall x\geq 1$: $$\left|\sum_{n\leq x} \chi(n)\right|< \sqrt{k}\log k,$$ that is, the sum remains bounded when $x\to\infty$. My question is: what is the behavior of $$\left|\sum_{p\leq x} \chi(p)\right|,$$ when $x\to\infty$ ?
Notice that this is a whole different animal since with Pólya's inequality we had the periodicity of the Dirichlet characters over the natural numbers, whereas no such simple property holds if we restrict the sum to only prime numbers.