The doctrine of original intent rests on a set of implicit assumptions about the framers as a breed apart, momentarily allowed access to a set of timeless and transcendent truths. The doctrine requires you to believe that the "miracle at Philadelphia" was a uniquely omniscient occasion when 55 mere mortals were permitted a glimpse of the eternal verities and then embalmed their insights in the document.
No originalist, I suspect, would recognize this as his viewpoint. None with any scholarly credentials would dare say that the Framers were "momentarily allowed access" in such a passive sense, as if they had received a revelation from a higher power. The originalist position, as I understand it, gives the Framers more credit for agency and original thought. The main difference the originalists posit between the Framers and today's jurists and politicians is that they presume the Framers, generally speaking, to have been philosophers engaged in an inquiry into the ideal form of representative government, the one best suited to a notion, likewise philosophically rooted, to individual human nature. Originalists presume the Framers to have been guided by a concept of unchanging human nature and natural right toward discovering, rather than inventing, the form of government, compromises notwithstanding, that is best for all people at all times. By comparison, originalists accuse activists of being driven by self-interest (i.e. political gain) or unsustainable concepts of "fairness" instead of any long-term notion of justice.
While I wouldn't be so contemptuous toward originalists as Ellis is, he's right to state that their idealist understanding of the Framers' work isn't backed by facts. It doesn't take much reading on the making of the Constitution to see that the Founders had set themselves to solving a specific political problem, not a universal one: how to maintain a federal state with multiple layers of representative government across a large territory. Much of the polemical or op-ed literature in defense of the Constitution was meant to refute the idea, popularized by Montesquieu, that a republic could not govern a large territory, but would inevitably collapse or turn into a tyranny. Federalist Paper No. 10, written by Madison, is key to understanding how the Framers tailored their work to a specific challenge. Madison envisioned a federal republic of sufficient size and diversity that no single interest group could end up dominating the others. Eliminate the size and the diversity and he might have proposed a different form of government altogether. The Constitution does not represent a "one size fits all" political philosophy. Since it was a do-over of the Articles of Confederation in the first place, it's obvious that within a single generation the Founders adapted their notions of ideal government to changing circumstances after their first draft proved inadequate in practice. They didn't expect their second try to be jettisoned entirely as the Articles had been, but they did provide for amendments in a manner belying any assumption that the document ratified in 1788 was a permanently perfect frame of government. The mere fact of an amendment provision makes clear that the Framers themselves didn't think that their original intent would be the final word on the question of representative government. The only point originalists can make legitimately is that any overruling of the Framing intent should be done through amendments rather than through legislation or judicial rulings. Even on that point, however, the almost immediate polarization of the Framers into Hamiltonians and Jeffersonians made the meaning of the Constitution a matter for perpetual debate, with leading Framers on both sides of many disputes. A 21st century appeal to original intent begs the question whether one means Hamilton's intent, Madison's or someone else's -- and how does one choose among them? And if the actual authors of the Constitution ended up disagreeing on its scope and limitations, why should their conflicting opinions automatically overrule those of moderns interested in applying the mechanics of the Constitutions to problems the Framers never anticipated?
Ellis cites Thomas Jefferson as a debunker of originalism, though it should be remembered that Jefferson had no hand in writing the Constitution and may well have been expressing sour grapes in the following:
Some men look at constitutions with sanctimonious reverence, and deem them like the ark of the covenant, too sacred to be touched. They ascribe to the men of the preceding age a wisdom more than human, and suppose what they did beyond amendment. ... Let us follow no such examples, nor weakly believe that one generation is not as capable of taking care of itself, and of ordering its own affairs ... Each generation is as independent of the one preceding, as that was of all which had gone before.
You can also tell that Jefferson is writing about amending constitutions, not interpreting them, but he makes Ellis's larger point, which is that the Framers, however superior in some respects they were to our present political class, don't have a veto on progress. Nor did they intend the Constitution as a permanent veto on progress, and as each Framer interpreted it according to his own values and interests, so should conscientious people today. The Framers intended the Constitution to outlive them. Common sense should tell us that their original intent was not to leave people 200 years later asking what they, the Framers, wanted future generations to do, but to figure out for themselves what the Constitution empowered them to do.