Thomson ReutersWASHINGTON (Reuters) - It is a political practice nearly as old as the United States - manipulating the boundaries of legislative districts to help one party tighten its grip on power in a move called partisan gerrymandering - and one the Supreme Court has never curbed. That could soon change, with the nine justices making the legal fight over Republican-drawn electoral maps in Wisconsin one of the first cases they hear during their 2017-2018 term that begins next month.