Former President Bill Clinton sounded frustrated about his value to his wife's presidential bid on the campaign trail in South Dakota on Friday.

The ex-president took a moment to ponder his lot in life onstage, and revealed the exasperation he has experienced stumping for Hillary Clinton.

"I sometimes feel that I'm totally useless in this election season because I'm a happy grandfather. I'm not mad enough at anybody," Clinton said. "And because the life I spend now is driven by the real world and facts. I mean, we live in kind of a fact-free political universe, you know?"

The 42nd president's remarks come after Donald Trump, the presumptive GOP nominee, has repeated "rape" allegations against the former president and suggested Hillary Clinton would want to keep her eye on her husband if they got back to the White House.

In response, Hillary Clinton chose not to challenge Trump's assertions directly and told CNN "He can say whatever he wants to say" about her husband.

The former president's comments suggested he recognized that his congenial tone was not in demand this election season and could become a detriment to Hillary Clinton as the 2016 race progresses.

While the former president is stumping in the Mount Rushmore State, Hillary Clinton is fundraising in Texas.