Between 1787 and 1840, the Constitution gained a far more democratic meaning than it had had at the Founding, and Thomas Jefferson was a key figure in the process of democratization. But, while more democratic in inclination than many of the Framers, he fell far short of the radically democratic constitutionalism of his most important acolytes, Martin Van Buren and Andrew Jackson. Jefferson was actually much less attached to democracy and more to law as the heart of the republican Constitution. Compared to the 1830s founders of the nation’s democratic Constitution, Jefferson retained much of the elitist, law-oriented, anti-party, slavery-protective (though not pro-slavery) convictions of most of the Framers. In practice, his constitutional politics as Republican leader in the 1790s and president in the 1800s built an important bridge to the democratic Constitution of his successors, even if he never fully embraced that development. The ascendancy of the Jacksonian Democratic party would entrench essentially Jeffersonian constitutional principles of states’ rights and slavery protection but would substitute democratic will for reason and law at the foundation of the Constitution.I believe Leonard's thesis is amply supported by excellent contemporary historical research. See, for example, Gordon S. Wood's Empire of Liberty: A History of the Early American Republic, 1789-1815 (an earlier post here), Charles Sellers's The Market Revolution: Jacksonian America, 1815-1846, and Susan Dunn's little-known monograph, Dominion of Memories: Jefferson, Madison and the Decline of Virginia (previous post here).
In other words, even accounting for Jefferson, the "Founders" were most certainly anti-democratic but it was Jefferson's inconsistent elitism that paved the way the early nineteenth century "revolution from below." And it's that revolution--the democratic one--whose success bathes all current political thought in the antinomies of democratic constitutionalism.