Alexandra Rojas was shocked. So was Waleed Shahid.

The two vocal leaders of Justice Democrats, an advocacy group whose uncompromising style has made it a nuisance among Washington traditionalists, had a meeting request from aides to Senator Elizabeth Warren, who was fresh into her presidential campaign. As Ms. Warren sought to push the party to the left by proposing expansive liberal policy ideas, her team was prepared to seek counsel from organizations that did the same.

“They want us in their court,” Ms. Rojas said. “They know that if they want to win, they need to have the support from the grass-roots energy.”

Ms. Warren’s willingness to look outside the traditional pool of political aides underscores the extent to which activism and ideology are shaping the makeup of campaign staffs for Democratic candidates, even at the highest levels. Neither Ms. Rojas nor Mr. Shahid received a job offer, but in a crowded field where candidates are looking to stand out, activists fluent in the language of social movements are gaining value as important allies.

Julián Castro hired as his campaign manager Maya Rupert, a campaign novice who made her name in organizing with the Center for Reproductive Rights and the National Center for Lesbian Rights. Senator Bernie Sanders has expanded his close-knit group of strategists and tapped Faiz Shakir, the former political director for the American Civil Liberties Union, to run his new-look presidential campaign.