In a governmental system where rulers are chosen by elections, the rulers will reflect the moral values of the people, or those among us who can exert the most pressure on the electoral process. If the moral values decline, then so will the value of the leaders. They will find ways to subvert--or will simply ignore--the checks and balance system of the constitution in order to impose the kind of government they want.
So...why do you think that the checks and balance system began to break down so quickly? First the national government taking power from the states, and then with the various branches of government dominating the other? I don't think the framers of the constitution ever envisioned such an event...so what happened? I place my bets on who has sovereignty.
Yes yes, the old "the worlds going to the devil in a hand basket" argument, which there has always been a certain amount of the people, in every generation, since the beginning of the country making that claim.
So has does one make the determination that the moral value of the country is in decline?
In the state where I live years ago we use to have a law on the books that mandated that one was not allowed to go outside of the boundaries of there home on Sunday morning before noon, unless the were going to church. Eventually the law was repealed and people could go wherever they wanted on Sunday morning.
So does this represent a decline in moral values because people were no longer mandated by law to be setting in church on Sunday morning fearing God, or being a prisoner in there own homes? Or does it represent a rise in moral values because some people made a stand for their rights of freedom and the ability to determine where they wanted to go on Sunday morning?
I'm sure it would depend on who you ask.