Can political parties retain control over party nominations when candidates are selected through primary elections? As parties in new democracies increasingly open up their candidate selection processes to mass participation, existing literature has been skeptical as to the ability of parties to retain their influence over who will be chosen to represent the party at the ballot box. Contrary to this skepticism, I argue that parties remain key players despite the introduction of primaries, and that party leaders are able to obtain their goals by leveraging their persuasive influence over primary voters. I test this argument using original data on party endorsements and nominations as well as an experiment on primary voters in Kenya. Results suggest that parties can critically shape primary outcomes using endorsements, and that primary voters utilize endorsements to make inferences about a candidate’s electoral prospects and ability to deliver local development.