The tabloid Daily Mail thinks it is. They ran a big story here.
Doug Emhoff (photo) admits he cheated on his first wife, but according to Politico, Harris knew about it she married him, and the Biden campaign knew about it when vetting Harris for vice president (see story here).
“The incendiary news is said to be causing panic in Harris’s campaign,” Daily Mail blared. There are no signs of that, and I don’t know why it would affect the campaign any more than Trump’s many affairs do.
Maybe you could argue Democratic voters demand more morality of candidates than Republican voters do, but that’s speculative (consider, e.g., Bill Clinton). And anyway, it wasn’t Harris who cheated; Emhoff isn’t running for anything, although if she’s elected he’ll likely have some First Lady duties.
Harris and Emhoff married in their late 40s, so of course both have prior histories that include other relationships. In any case, it’s old news. The affair happened years ago.
Today, Harris and Emhoff are on good terms with his ex-wife, and his former mistress has a $1.4 million house in The Hamptons. Everybody’s happy, including the Daily Mail publisher. The principal value of this non-earthshaking story is it boosts their circulation.