First of all, no Declaration of Indepedence is not just ideal philosphy, it's an legal document, an contract between US and it's people.
1, It outlines the tyranny of tax imposed
2, It defined the minimum inalieanable rights of any individual ( any person).
First of all, I didn't say that the Declaration is "ideal philosophy." But, it's not a legal document, you're confusing it with the Constitution. The Declaration listed the reasons that the colonies should be independent. It's called "the long train of abuses" and in fact "taxes" are only mentioned in one sentence. Go here for the actual document, then come back and talk. It's all there.
https://www.ushistory.org/declaration/document/Of the tyrannies of King George, taxes weren't the biggest. Absolutely no colonist would risk his life over a three cent tax on tea. Yes, the Declaration declared certain inalienable rights were granted by God, but the colonists had no problem taking those rights away from the majority of the population. Like I said, read the document, then let's talk specifics.
In truth, US is actually a republic. And Declaration of Indepedence is really the last line of defence.
So, you declare the Truth, but who said anything about whether the US was a democracy or a republic? Anyway, the only people for which that distinction would make a real difference are political scientists. I'm serious. Ancient Greece invented democracy, but they practiced slavery. I think you're making the distinction in order to say something else. I've seen bumper stickers with the phrase "Give us back our republic," and I have no idea what they mean. For ex.,
Republic: "A state in which supreme power is held by the people and their elected representatives..." Democracy: "A system of government by the whole population or all the eligible members of a state, typically through elected representatives."
So, please explain why the distinction is important or practical when it comes to the US.