The answer is D. Intergroup
Explanation
We know it's not A.) Because this conflict was between the two parties so we know it is not within oneself
We know it isn't B.) Because this wasn't within the group of Republicans and Democrats this is talking about between Republicans and Democrats
We know it isn't C.) Because Intragroup is between members within the group
That leaves D.) Intergroup which by definition is between two or more groups so D is your answer