I didn’t mean to suggest there was no German identity retained at all; just that they assimilated more rapidly and to a greater degree than most other immigrant groups.
Some of this may also have been due to the fact that so many emigrants became farmers. Although there certainly were German neighborhoods in urban areas, I don’t think they formed enclaves to the extent that later immigrants like the Irish, Italians, and Jews did.
Dutch more than German.
According to wikipedia a quarter of British troops in the Revolutionary War were Germans. George III was a German too. So they might not have been too popular with the Founding Fathers.
The Christmas tree is German in origin, as are many of our Christmas carols.
Why do you say more Dutch than German? There were both Dutch and German immigrants, and they both brought with them their traditions of Santa Claus. The Germanic traditions of the Yule log, the Christmas tree, Christmas ornaments, and the Christmas ham showed up here too, suggesting that the American Christmas is at least as much German as Dutch, and perhaps more so.
Part of it is certainly that the German states lacked a shared political history. England had been refining its political system for centuries and there was an established tradition of political science dating back to the 1600s. Germany doesn’t have anything like that, with fragmented principalities with different systems of law and government and little tradition in political thought.
Some Germans did have an influence, as well. Zenger, one of the US’s first free speech advocates, comes to mind. His advocacy probably had an effect on the inclusion of free speech in the Bill of Rights much later.
Little influence, or little apparent influence ?
In the UK the English do not bang on about the influence of their Anglo and Saxon forebears, let alone the later Hannoverians. Yet Saxon Law ‘absorbed’ the Norman and Danish cultures.
I think, much like the “why are there so few German restaurants?” thread, the answer is that the German people were so influential so early and *also *so assimilative, that we’re surrounded by German inspired culture and thought and think it’s “just American”. It’s like water in an aquarium to a fish - he doesn’t feel wet because it’s always there. It took us centuries to figure out that air isn’t nothing, because it’s always all around us.
Of course, I say this as a girl from Brementown in Tinley Park (formerly known as Bremen) who went to Keller Elementary, studied with Mr. Funk, Mr. Rader, Ms. Shapiro and Mrs. Becker, lived on the same block and the Fischers as the Shaeffers and saw more Bettenhausens on the police force and fire crews than you can shake a German stick grenade at. 
On the contrary, just because the Holy Roman Empire does not match our twenty-first century conception of a nation-state does not mean that all those German principalities did not have extensive experience of shared representative bodies and law courts. Indeed, precisely because the powers of those imperial institutions were so often contested, Germany in fact had traditions of political thought at least as well-developed as those of the British Isles. Many specifically German concerns, such as the role of common institutions within a confederal system, had clear American resonances.
There is also no doubt that these German debates about the structures of the Empire were well-known in America. To put it very bluntly, anyone in the eighteenth century with an interest in political theory had read Pufendorf. His ideas were central to any discussion of natural law theory. One really need look no further for a very obvious example of a German thinker whose works influenced (positively and negatively) the intellectuals of the American Revolution.
But none of this depended on the presence of German speakers in America. Pufendorf’s works had long before been translated into English. The works of many other German jurists were also accessible in Latin.