Newsom's campaign ad is 30 seconds, and the word is -- he bought airtime on Fox News in Florida markets for this cheeky spot, set to run through the holiday weekend. It's pretty funny, 'cause GN's embracing rhetoric the right often use, including "taking your freedom."

Check it out ... the Gov. is addressing Floridians directly, telling them that their freedom and rights are under attack in their state -- via book banning, voting restrictions, limiting speech in classrooms, as well as criminalizing women and doctors (a la the new abortion ruling).

He goes on to say that he urges everyone living in the Sunshine State to "join the fight" ... by coming over to California, where he says the idea of freedom is still very much alive.

The whole thing is super ironic and full of satire -- and Newsom's getting a lot of praise online for going out of his way to stick it to DeSantis (seen as an up-and-coming star in the GOP) and right-wingers generally. Others, however, are raising an eyebrow over this.

Some have noted this stunt -- which has no bearing on his re-election chances in November, since no one in Florida can vote here anyway -- was expensive ... and probably unnecessary.

So, why do it??? Well, as political pundits have articulated ... Newsom seems to be ambitious beyond just California politics, and may be trying to lay the groundwork as a go-to Dem voice on the national stage in the not-too-distant future. He also probably sees DeSantis as a good foil ... because he too is seen as a GOP leader going forward, post-Trump.