Unknown candidates do not have any particular name. People will announce are running. Some are nominated by obscure parties and are put on the ballot in some states. Third parties candidates sometime attract a significant number of votes, but they are hardly unknown. A darkhorse is a candidate who was not expected to win the nomination, but is nominated by a major party.That may the term you are thinking of.
The vice presidential candidate is often referred to as the running mate of the presidential candidate during the campaign.
Presidential Candidate
They are called the party's presidential ticket. Also the party's presidential nominees.
The word "secede" seems strange here. People say a candidate withdrew or dropped out of the race, if he stopped seeking the nomination.
"dark horse"
Voters who have not decided are called undecided.
Voters who have not decided are called undecided.
Bill Clinton.
Losers usually make a concession speech, conceding defeat by the other candidate.
Attract more voters for the presidential candidate
The candidate for vice-president is nominated at the same national convention that nominates the presidential candidate.
Any American can make campaign contributions to a presidential candidate.