Donald J. Trump’s campaign experienced two more departures this week when two staff members who handled surrogate operations resigned, including one who was hired less than two weeks ago.

Kevin Kellems, who was hired on June 20 to oversee the campaign’s surrogate division — supporters on the team who defend Mr. Trump and promote his message publicly — resigned on Thursday, and Erica Freeman, who similarly dealt with surrogates, also quit.

In his resignation letter, which was shared with some staff members, Mr. Kellems acknowledged just how short his stint with the campaign had been.

“While brief, it has been an interesting experience, and am proud of the contributions made through our early-phase project endeavors,” wrote Mr. Kellems, who advised former House Speaker Newt Gingrich during his 2012 presidential campaign and also served as the communications director for former Vice President Dick Cheney.