What's the meaning of "lock up the nomination"

Question

The campaign aims to lock up the nomination in March regardless of any early setbacks in Iowa. -NY Times-

What's the meaning of "lock up the nomination" in this sentence?

Answer 1

Lock Up The Nomination in terms of how it is being used in the NY Times means to win enough delegates in State primary elections so as to not have any challenges in the nominating process during the party's convention.

Each US State has rules on how delegates are allocated to Presidential candidates during primary elections. These delegates are selected by the State's political party to represent the party at the National Convention. While each delegate is supposed to have an individual nominating vote at the National Convention, in practice, their participation is just a rubber stamp of the outcome of the primary election for that State.

Delegates also participate in the formation of the party platform and the nomination of the Vice Presidential candidate, but for the most part the Vice Presidential candidate chosen is the person picked by the Presidential nominee.

So the advantage of "locking up the nomination" by March basically means that the candidate will have gained more than the necessary number of delegates to win the nomination at the national party convention and means that they can refocus their campaign to address the other party's major candidate, as opposed to having to hold off challenges from within their own party.

Answer 2

The term lock up, according to Oxford Dictionary refers to...

The action of becoming fixed or immovable.

In other words, to "lock up the nomination" is to secure it; to ensure a specific end-result that is fixed or immovable.