Why, it is consonant with Romans 13. Insofar as the current US government protects justice as expressed in the Ten Commandments and similar precepts of moral theology, and is not a "terror to good works" it is legitimate.
The US government is not consonant with Romans 13. It does not protect justice as expressed in the Ten Commandments, it is not consistent with similar precepts of moral theology and increasingly so, is a terror to good works.
Now give us your judgement.
Well, it seems that we agree on the legitimacy of the US government. Note that the said legitimacy, or lack of it, has nothing to do with who elected who, when and how, and what the Constitution has to say about the process.
My advice to all Catholics and in fact all Bible believing Christians is to support the government when it is doing something right, ignore it when it is not, resist it when it does some direct evil like removal of religion from the public square and baby-killing, and try to do what is moral as if no government existed. In other words, my advice is to behave like free people do.