The dueling political events on Tuesday were as discordant as they were separate: The president and his first-term secretary of state sidestepped the email issue at their rally, where Mr. Obama clasped hands with his onetime rival and predicted victory in the fall, making no mention of Mr. Comey’s dramatic announcement in Washington faulting Mrs. Clinton even as he recommended against criminal charges.

Without mentioning the email controversy, Mr. Obama pointed to the political attacks that have chipped away at Mrs. Clinton’s trust among voters. “Can I be blunt?” he said. “Hillary’s got her share of critics.” But, he added, “That’s what happens when you dedicate yourself to public service over a lifetime.”

Mr. Obama delicately touched on Mrs. Clinton’s perceived weaknesses as a candidate even as he marveled at her tenacity in the nominating fight they waged against each other eight years ago. In an election year in which outsider candidates have railed against the establishment, Mr. Obama portrayed Mrs. Clinton’s decades-long experience as a plus.

“Sometimes we take somebody who has been in the trenches and fought the good fight and been so steady for granted,” he said, recognizing that voters’ yearning for the next new thing had helped his own 2008 campaign. “We don’t do that, by the way, for airline pilots.”