[KarlInOhio]

How would you determine the D or R for members of the Democratic-Republican party before 1820?

I would either put DR for the full name, or just D because it was the direct predecesor of the current Democrat party. I would not use just R. I hate to get out the tin-foil hat, but I don't think that this could be accidental.

[jae471]

I doubt its worthy of tinfoil. Jefferson called himself and his party Republican. From his first inaugural address "We all are Republicans; we are all Federalists."

"Democrat" wasn't really used until after true parties were formed.