Jennifer Newsom Slams Donald Trump for Mocking Husband Gavin's Dyslexia

8:51 AM PT -- White House Spokesman Davis Ingle tells TMZ ... “President Trump is right. Gavin Newscum is the worst governor in America, and he also may be the dumbest.”

Jennifer Newsom is going full scorched earth on President Donald Trump after he came for her husband, the governor of California ... declaring she’s not letting a dig about dyslexia slide.

In a fiery IG video Monday, Jennifer shut it down fast, saying learning differences don’t define someone’s potential, but mocking them sure says a lot about you ... calling Trump’s comments offensive and ignorant.

Jennifer doubled down, pointing out people with learning challenges work twice as hard to prove themselves -- then flipped it, saying the one who’s actually unfit is Trump … and rattles off a list of facts about him she says prove it.

She rounded out the whole thing by slamming the Republican Party for "normalizing this vile specimen of a human being."

This all comes after Trump took a swipe at California Governor Gavin Newsom in the Oval Office Monday -- calling him "low IQ" and saying he’s "all for people with learning disabilities, but not for my president."