WASHINGTON — Former Vice President Mike Pence is planning to fight a subpoena by the special counsel overseeing investigations into efforts by former President Donald Trump and his allies to overturn the results of the 2020 election, according to people familiar with his thinking.Pence and his attorneys are planning to cite constitutional grounds as they prepare to resist special counsel Jack Smith’s efforts to compel his testimony before a grand jury. They argue that because Pence was serving in his role as …