Republican presidential front-runner Donald Trump, increasingly focusing on Hillary Clinton rather than his GOP rivals, says he's not concerned by reports Bill Clinton will soon hit the trail for the Clinton campaign.

"I think that Bill Clinton turned out to be a liability against Obama when [Hillary Clinton and Barack Obama] ran against each other in 2008," Trump said Sunday morning on "Fox and Friends." "If you look at that whole campaign, it was a mess. [Bill Clinton] said things that were very problematic and troublesome ... certainly Bill Clinton is not going to be the end-all in the campaign."

Trump also explained his charge, made in a tweet Saturday night, that Bill Clinton has a "penchant for sexism." In the tweet, Trump said "Hillary Clinton has announced that she is letting her husband out to campaign but HE'S DEMONSTRATED A PENCHANT FOR SEXISM, so inappropriate!"

"The 'penchant for sexism' was exactly her words," Trump told Fox. Trump took the phrase from a recent Des Moines Register interview in which Clinton was asked about Trump's use of the word "schlonged" to describe her 2008 defeat. "It's not the first time he's demonstrated a penchant for sexism," Clinton told the paper. "Again, I'm not sure anybody's surprised that he keeps pushing the envelope."

Trump again explained "schlonged," saying "First of all, the term I used was not a vulgar term ... it means beaten badly ... that's what happened to her [in 2008] ... that was a race that she was expected to win."

Finally, Fox asked Trump about Republican Rep. Trey Gowdy's decision to endorse rival Marco Rubio. "I hope [Gowdy] does a better job than he did, frankly, at the Benghazi hearings, because they were a total disaster," Trump said, referring to the heavily-watched hearing in which House Benghazi Committee Chairman Gowdy called Hillary Clinton to testify last October. "[Gowdy] did not win with those hearings. ... It was not good for Republicans and for the country. I hope he does a lot better for Marco than he did with the Benghazi hearings."