Most of the money for preconvention campaigns for presidential candidates comes from

from the super PAC (special political action committees.)

Explanation:

The major source of campaign financing is the Super PAC, the special political action committees.this organization is allowed by the Supreme Court to spend unlimited amounts of money on their preferred candidate. The money spent by Super PACs is part of a presidential campaign, although it does not represent money spent by the candidate.

freedom of speech is also protected by the 1 amendment.

explanation:

here is pretty much what the 1st amendment says:

congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances.