Fact checking a political ad?
Null program. Political ads are made from 100% artificial ingredients and completely devoid of "facts" by their very nature.
It's a steep slope if any platform is made to "fact check" advertising and user submitted material unless that platform is a co-author or is supporting the statements made. If they had to verify every ad, they'd also need a products testing lab to ensure that the detergent that claims it gets whites, whiter than ever before, it does. They also have to verify that the new chicken sandwich from brand A is 20% more tastier than brand B. Will magazines and newspapers (those remaining) have to do the same thing? TV networks?