Usually the candidates don't start getting official secret service protection until after the convention, when there is one official candidate from each party, although sometimes the president will authorize security for a high profile candidate or one who is obviously the frontrunner.  Of course the sitting president is always protected, and in this case Biden as a former vice president would have secret service protection.  I think that any senator or representative would likely have a state policeman or two plus whatever privately hired security he wanted.