Consequentialism always winds up devouring itself, and this is why:
STEP 1: Define the “Good”
That act is good which causes the most net [here insert synonym that allows one to pretend the statement is not a tautology, e.g. human flourishing, increased wellbeing, etc.].
What causes the most [net increase in flourishing]? Since there is no standard for determining it, it amounts to a subjective call based on the person’s preferences in every instance.
Thus, the good is ultimately defined as the “desirable” and the “desirable” is that which one actually, at any given moment, desires.
STEP 2: Free Oneself From Limits
If result X is the good result (see above definition of “good”), what means may one employ to achieve X?
The good must be achieved by any means necessary.
STEP 3: Combine Steps 1 and 2
One may act to achieve that which, at any given moment, one desires by any means necessary.
So, for example, if one thinks Trump is going to win in 2020 in a free and fair election, and one believes it would be “good” for Trump to lose, then one is not only justified in rigging the election to avoid that result, one is morally compelled to do so.