Herman Cain speaks at the Virginia Tea Party Patriots Convention in Richmond, Va., on Oct. 9, 2010. Cain holds up a copy of the United States Constitution, emphasizing the theme of the convention: "The Constitution Still Matters." (By P. Kevin Morley/Associated Press)

We don’t need to rewrite the Constitution of the United States of America, we need to re-read the Constitution and enforce the Constitution. … And I know that there are some people that are not going to do that, so for the benefit of those who are not going to read it because they don’t want us to go by the Constitution, there’s a little section in there that talks about “life, liberty and the pursuit of happiness.”

That bit about “life, liberty and the pursuit of happiness” is from the Declaration of Independence, not the Constitution. So perhaps “some people” aren’t the only ones who need to re-read our founding documents.

But Cain isn’t the first to make this mistake. During health-care reform, then-minority leader John Boehner took to the steps of the Capitol to argue that the ghost of George Washington would clearly vote against the Affordable Care Act. “This is my copy of the Constitution,” he said, waving it in the air, “and I’m going to stand here with our Founding Fathers, who said, ‘We hold these truths to be self-evident, that all men are created equal, that they are endowed by their creator with certain unalienable rights, and that among these are life, liberty and the pursuit of happiness.’ ”

Mix-ups happen, of course, especially when you’re speaking off-the-cuff. But here’s what I don’t get about the affection Cain and Boehner show for these particular lines: In general, conservatives wield the Constitution to argue for a narrow, limited view of federal power. Tenth amendmentism, you could call it. But the preamble to the Declaration of Independence is incredibly expansive. A “right” to “life, liberty and the pursuit of happiness” could easily be interpreted to include a right to health care, for instance. It could be interpreted, in fact, to include, or rule out, most anything. “Life, liberty and happiness” are not legally precise terms.

Which makes sense: the Declaration of Independence was written to justify a break from the British, not to define the powers of the federal government. But it’s fairly consistently trotted out by conservatives to show that the simple act of reading “the Constitution” proves that the contemporary conservative take on policy issues is constitutional while the contemporary liberal take is unconstitutional. I think that goes to show how seriously you should take that claim, but I think it also goes to show how seriously they take that claim. After all, it’s perfectly clear how a conservative could read the 10th Amendment (while ignoring the “Necessary and Proper” clause) and decide that, say, Medicare is fundamentally unconstitutional. But it’s impossible to see how anyone could seriously read the preamble to the Declaration of Independence and walk away thinking, “That definitely supports my political preferences, and definitely rules out everyone else’s.”