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Charlie Neibergall, Associated Press
Republican Presidential candidate Sen. Rand Paul, R-Ky. speaks during a rally at the University of Iowa, Friday, April 10, 2015, in Iowa City, Iowa.

WASHINGTON — President Barack Obama had some advice for Hillary Rodham Clinton in the days before the launch of her presidential campaign. If she's just herself, he said, she'll do fine.

But plenty of politicians — Clinton among them — have found it tricky to just be themselves in the maelstrom that is a presidential campaign.

Clinton in her 2008 primary campaign projected strength, then empathy. In the 2016 Republican race, Kentucky Sen. Rand Paul is trying to rein in some testy tendencies that are part of who he is.

A veteran of four Republican presidential campaigns, Dan Schnur, says being yourself is no easier for presidential candidates than for anyone in a job interview. It's only human nature, he says, to stretch who you are to impress others.