A political party chooses its candidate for president at a

Answer: Political party's candidates for president are choosing at nominating convention

Explanation: Nominating convention is a political convention held every four years in the United States by most of the political parties in order to select the party's nominee for President, as well as to adopt a statement of party principles and goals known as the platform and adopt the rules for the party's activities, including the presidential nominating process for the next election cycle. At the convention, a body of delegates, voting representatives from each state, will cast votes for a nominee until a winner is selected. Afterwards, the presidential candidate will select a vice presidential candidate to be his/her running mate.