The veneration of the founders has its origins in the founders themselves, but their general veneration did not reach the manner to which we are accustomed until after their deaths. Most of the founders were subject to blistering political attacks even before 1776.

We can't forget that the American political vision was contested at the start amongst the founders. An angry public discourse sprung up around the ratification of the Constitution in which the Antifederalists and the Federalists both accused each other of being traitors to the real American vision, which was invariably their own. We should note that the early republic was on very shaky ground and the public was anxious about whether or not it could stand the test of time. This anxiety often manifested by asserting that one's political opponents would cause the collapse of the whole enterprise.

The early Federalist and Democratic-Republican parties both had their the support of politically-aligned press that served as unofficial organs for their parties. Alexander Hamilton, for example, was commonly referred to as Washington's bastard son or as being half black because of his Caribbean birthplace (sometimes both). Both sides of this emergent political spectrum had a vested political interest in venerating their own leaders while denigrating their rivals.

The famously vitriolic language of the Election of 1800 between Thomas Jefferson and John Adams stands as an example of how divided political attitudes were at the time and how those political divisions translated into an personal attacks on character that were carried out in public via the presses. The press was a vehicle of the political elite, but it was consumed widely. The American people turned to the press most closely aligned with their own political beliefs in the early years much as they do now via the Internet. Echo chambers were the norm, not a departure.

There are cases within this paradigm that should be noted. George Washington was not subject to the same level of personal attacks as other founders. He had something resembling a cult of personality as a result of his leadership during the American War for Independence. This was manifested most prominently via the Society of Cincinnatus, which was created to honor those who fought for the nation's freedom and named in honor of Washington himself (Washington stepped down from power after the war and American politicians were quick to draw parallels to Cincinattus, a Roman general famous for doing the same). Washington himself took pains to cultivate this image, casting himself as having sacrificed his health and his best years in service to the country.

Even though Washington was subject to more deification in his lifetime than his contemporaries, he did not escape a public dialogue that attacked him as a human being. The Conway Cabal was a movement within Congress to have Washington replaced during the Revolution due to a fear of his popularity among the people and murmurings of his incompetence. These murmurs fell silent after 1781 with the victory at Yorktown, but rose anew when he was confirmed as the first President of the USA. Early public dialogues tended to avoid direct personal attacks in favor of attacking his political allies, Alexander Hamilton most notably, who were depicted as snakes whispering lies into the president's vulnerable ears. But the attacks became more personal as time went on, casting Washington as either a senile old man or a would-be tyrant. Washington's farewell address decried the political dividedness of the USA and issued warnings against it, but we should consider that he made these comments in the context of political attacks on his own person.

These attacks died with Washington's departure from office but took the step towards deification with his death in 1799. His death prompted an outpouring of grief from the American populace that elevated him above the messy political realities of his career. This process tended to repeat after the deaths of the important founders, but reached a crescendo after 1825 with the deaths of John Adams and Thomas Jefferson. Their deaths coincided with and fed into an upswell of nostalgia for the nation's origins now that it found itself on mostly stable footing. The public dialogue confirmed that the USA was both a success and a positive good for the world and for human liberty. It was expanding rapidly via the Louisiana Purchase and its economic fortunes continued to grow. This general sense of optimism was projected backwards onto the founders (conveniently after most of their deaths), generating a deep nostalgia for America's origins as a nation-state and for the men held responsible for bringing it about. In many ways, the enthusiasm that went into eulogizing the founders had the additional effect of deifying both the founders and the nation itself.

Of course, this is simply where the general deification began. It has its origins in the political discourse that sought to elevate certain individuals and carried forward some of those tropes, but the act of co-opting the founders for one's own political agenda continues to change and shift, ebb and flow, through time into the present and beyond. The process began during their lifetimes, intensified after their deaths, and continues to evolve this very day.

Edit: Added a sentence to the penultimate paragraph.

Sources:

• Ron Chernow - Washington: A Life

• Ron Chernow - Alexander Hamilton

• Andrew Burstein and Nancy Isenberg - Madison and Jefferson

• Andrew Burstein - "Immortalizing the Founding Fathers: The Excesses of Public Eulogy," in Mortal Remains: Death in Early America (pp. 91-107)

• James Sharp - American Politics in the Early Republic : The New Nation in Crisis

• Heike Paul - The Myths That Made America: An Introduction to American Studies