A couple of additional, and short points:

First, a "constitutional republic" and a "representative democracy" are the same thing. Full stop. Conservative commentators like to run out that phrase as if it means something special and refutes the United States being a "democracy." That is rhetorical legerdemain. When the founders used the phrase "republic" they meant "representative democracy" - "a state in which supreme power is held by the people and their elected representatives, and which has an elected or nominated president rather than a monarch." See Webster. Sounds like democracy, doesn't it?

What this trick is intended to do is obfuscate and confuse. What is usually intended is to create confusion about the United States as a federation, elevating the interests of States over the central government, which is both historically and functionally inaccurate (in short, deceptive). [It also conveniently replaces "democrat"ic with "republic"an.] The Constitutional Convention replaced the Articles of Confederation, which had a weak central government dominated by individual colonies, and was universally considered unworkable. The new Constitution created a strong, indeed, "Supreme", central government. That is the reality these commentators wish to hide.

Second, the principle purpose of the EC was not to thwart the "plan of the convention". It was intended to create a workable mechanism to establish an Executive that represented all of the people of the United States, and NOT the parochial interests of the constituent States. At the time universal suffrage was neither practical nor desirable. That is why the "college" meets in the different States the reports to Congress. Travel, even communicating, was incredibly slow. As with all other aspects of the Constitution and the preferences of its adopters, it was created as a representative constituency, not as a functionary of individual State interests.