I think you will find that the Founding Fathers of the United States were some of the most highly educated members of their society and were taking exceptional risks with an experiment in Republican and Constitutional Government that was unparalleled in the world at the time. The only comparable one was the
Corsican Republic (1755-1769) so it wasn't really certain they would succeed in creating a government, let alone one that would last more than two centuries.The Constitution was the
second attempt to establish an American government (after the Articles of Confederation) and was discussed in the Federalist and Anti-Federalist Papers. It would be extremely difficult to call the US constitutions anything other than an "intelligent, articulate, elaborate and insightful" document based on the most advanced political principles of its day. We can comfortably criticise the endurance of slavery, the abuses of native Americans and the growth of socio-economic inequalities by the late 19th century with the benefit of hindsight, but that should not under-estimate the achievement of establishing a revolutionary government.
The case for Communism and Socialism relies on understanding that the principles of the US constitution have been (perhaps) superseded by a much greater understanding of the forces governing social evolution, in the case of Marxism. I think it is disingenuous to expect that the Founding Fathers could have applied Socialist principles to the American Republic when Socialism didn't even exist as a coherent doctrine until the 19th century, with its earliest stirrings in the French Revolution of 1789. Socialism simply didn't exist in 1776, nor for that matter did Capitalism as an ideology as Adam Smiths Wealth of Nations was only published in that year.