Democrats jockeying to be Hillary Clinton's running mate defended the integrity of an inquiry into her use of a private email server while U.S. secretary of state, as the probe threatens wider fallout weeks before the political nominating conventions.

The vice presidential contenders swept Sunday morning talk shows to argue that a meeting last week between Attorney General Loretta Lynch and former President Bill Clinton on an aircraft in Phoenix would not undermine the email investigation.

Still, Sen. Sherrod Brown, a Democrat from Ohio, rued the optics of the encounter. "It was unfortunate," Brown said on ABC's "This Week." "I wished it hadn't happened, but I think the FBI will do its job."