CHICAGO — Chicago-area Republicans filed a federal lawsuit Monday alleging Illinois’ expanded vote-by-mail program is a “partisan scheme” to help Democrats get votes and could open the door to election fraud.The lawsuit is the latest GOP effort to curb mail-in voting, which President Donald Trump has called flawed and the greatest threat to his reelection. Though several states rely exclusively on mail-in ballots and fraud related to it is rare, it’s a complicated endeavor that more states are …