The word "unstinting" in the given sentence means generous, wholehearted, or without reservation. It suggests that the leader receives strong and unequivocal support from his party. Option C, "unsparing," is the closest in meaning to "unstinting" in this context. "Unsparing" also conveys the idea of not holding back or being generous and supportive, making it the most appropriate choice among the options provided. Options A, B, and D do not capture the positive and supportive connotation conveyed by "unstinting."