As Barack Obama and Mitt Romney fought for the presidency this fall, TIME contract photographer Marco Grob was crisscrossing the country to meet the men and women who may be doing the same four years from now.

From September to October, Grob, a Swiss photographer based in New York, traveled to 10 states and Washington, D.C., to shoot the 13 political leaders who comprise TIME’s Class of 2016 (Hillary Clinton and Andrew Cuomo were photographed earlier this year). “This series was very exciting because the fact that one of these politicians could be the next president was always on my mind,” says Grob, who took a variety of different kinds of shots and snapped extra rolls of photos to memorialize the moment.

Some of the subjects in Grob’s essay are American political royalty. Among the luminaries on TIME’s list are a First Lady (and now Secretary of State), a First Brother, six current and former governors and the current vice-president. Others, like San Antonio mayor Julián Castro and Florida Senator Marco Rubio, are rising stars – members of the fastest-growing demographic group in the U.S., men marked for higher office within their parties.

In the space of a single 48-hour stretch, the whirlwind assignment whisked Grob from Palo Alto, Calif., to Columbus, Ohio, to Baton Rouge. None of the subjects hinted at their political aspirations, and Grob preferred not to ask. “I don’t talk to them about their plans. I actually think it’s better if they don’t think I know much about their political careers,” he says. “They feel they can open up more.”

Breaking through that veneer of formality was one of the tasks confronting Grob, whose portfolio of portraits for TIME includes comedians and actors, world leaders and Ground Zero first responders. Politicians are trained are trained to stay on script. Grob’s challenge was to get them to veer from it. “Politicians, of all my subjects, are the most self-aware. They’re careful not to lose any voters, so they don’t get into anything controversial,” he says. His trick? “I always let them smile for a couple frames, but then I aim to make a more thoughtful portrait,” he says. “When you smile, you cover up your true face—that’s just what humans do.”

Alex Altman is a Washington correspondent for TIME. Follow him on Twitter @aaltman82.

Marco Grob is a contract photographer for TIME. View more of his work for TIME here or on his website.

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