Voters in Manteca and Ripon have a rare chance Tuesday to send shock waves reverberating through the Democratic and Republican party apparatuses. California’s open primary and the newly formed 10th Congressional District has created what many political observers believe ispendent to knock a major party off the November ballot. The district also includes Escalon and all of Stanislaus County At the same time, Lathrop voters in the newly drawn 9th Congressional District will have their say in a race that has attracted national attention.