Immunity does not equate to lack of opposition within government, which is what he is going to get if he plays by the rules. Now, if he goes in as commander in chief to depose them through a literal coup, he would be legally immune from the repercussions of abusing his powers whether it worked out or not, but the mistake here would be believing that the GQP care about legality when they only consider it a means to an end to corrupt so that the people that do care can't use it against them.