; and (B) may not be based on associations with any political party, incumbent, or political candidate, or potential political candidate. (3) Respect for counties, cities, and other political subdivisions. 4. Prohibition on partisan gerrymandering (a) Prohibition Except as necessary to comply with section 3(a), a State shall not establish a congressional districting plan that has the purpose or will have the effect of unduly favoring or disfavoring any political party. (b) Enforcement (1) In general Any eligible voter of a State may bring a civil action before a 3-judge court convened in accordance with section 2284 of title 28, United States Code, for a violation of subsection (a). (2) Court order A court in a civil action under this subsection— (A) may issue an order invalidating the congressional districting plan of such State on the grounds that the plan violates subsection (a); (B) shall consider any violation of section 3 to be probative evidence that the districting plan has the purpose of unduly favoring or disfavoring a political party