SPRINGFIELD — Republicans have claimed that state Sen. Sam McCann, who launched a third-party bid for governor this month, is “being used” by Democrats, setting him up to split GOP votes in November. As punishment, the caucus withheld his access to taxpayer-funded staff resources.But McCann, a Republican from Plainview, asserts he still has a constitutional right to party assets such as GOP photographers, bill summaries and web pages. And he is asking a federal judge to weigh in on the matter.McCann filed …