The Presidential Preference
Your first vote is for a Presidential Preference, or who you want to be the Republican nominee for President. It is the results of this vote that is used to determine how many delegates each Presidential candidate gets out of Tennessee.
Some states are "Winner-take-all", but Tennessee's delegates are allocated proportionally (unless one candidate were to get 2/3rds of the vote) so several candidates are likely to receive statewide delegates or delegates in any of our 9 Congressional Districts. A Presidential candidate must get at least 20% of the vote in either jurisdiction in order to get any delegates.
Let's say the statewide result were something like this example:
Tennessee Republican Primary
Ford and Hoover would not receive any delegates because they did not meet the 20% threshold. Delegates would be allocated based on the votes received by Lincoln, Reagan, and Eisenhower. Since 12 delegates are available statewide the distribution would be as follows:
Each Congressional District also elects 3 delegates. Essentially the first place winner gets two and the second place finisher in that district gets one delegate spot:
Additionally, Thirteen delegates are chosen by the Tennessee Republican Party's State Executive Committee and the three RNC members (our State Chairwoman, National Committeeman and Committeewoman) also attend the convention as delegates.
After you have chosen your Presidential preference, the Republican Party lets the voters decide which individuals get to represent their favored candidate at the Convention.
Essentially, delegates pledged to each Presidential candidate are running against one another in order to get a ticket to represent their man at the Convention. If, using the above example, Lincoln gets 5 statewide delegate spots; the top 5 vote-getting delegate candidates pledged to him will go to the convention.
Do I have to bother voting for delegates at all?
You do not have to vote for any delegates in order for your Presidential Preference to count.
You can just vote for the ones that are there, or vote for delegates for other Presidential candidates. It will not hurt your Presidential preference.
You have the option to vote for delegates who are pledged to candidates other than your own. Using the example above, lets say you are a Reagan supporter but you have a friend from church who is running as a delegate pledged to Lincoln. You can vote for Reagan, which helps him get more delegate spots, and vote for your friend under "Delegates pledged to Abraham Lincoln" to help him/her win the right to represent Lincoln at the Convention.