WASHINGTON — The Biden administration is rejecting calls from members of Congress for the United States to return to a campaign of maximum pressure against Venezuelan leader Nicolás Maduro after his chief political opponent was blocked from running against him. Speaking with a small group of reporters, a senior administration official said that the existing White House strategy of calibrating sanctions had produced results — despite the most recent setback — including the release of wrongfully detained Americans in the country and a diplomatic breakthrough in Barbados. “The approach that we st…