Question

Political parties first _____ to nominate presidential candidates.

asked political party contributors

held national conventions

held popular elections

used congressional caucuses

Answer 1

@Shadow

Answer 2

Before national presidential nominating conventions, back in the 1800s political parties first used congressional caucuses. They changed it after much debate about the Separation of Powers concern that correlated to the caucuses.
https://en.wikipedia.org/wiki/Congressional_nominating_caucus