A political candidate surrounds himself with factory workers in his new ad for
creating jobs.
Which persuasive technique is being used? (What is the BEST answer?)
Patriotism
Plain Folks
Testimonial
Name calling

He is likely using testimonial technique.

In ads that use this persuasive technique, people who use the service (in this case, people who will be affected by the creation of jobs), talk about why the product (in this case, the candidate), is good or beneficial for the general public.

While the ad doesn't necessarily seem to include workers talking about the benefits of the job creation, it is the closest technique.