If some of these kids get lost in the system and never returned to their parents, this better be the straw that breaks the camel's back for non-hardcore Trump voters that sticks in their craw until election day 2020. It better be a ongoing political set of commercial that airs consistently during 2020.
Spoiler: It won't be. Too much time, too little empathy, too easy to play off prejudices. Kids would have to die and that probably wouldn't be enough.
And that's if they are willing to believe it in the first place - I can't speak for hardcoreness but some Trump supporters are telling interviewers that they believe the pictures and video of child detention centers that the government provided
are all faked and Photoshopped. It's very hard to get people to change their mind when they've been conditioned to believe all undesirable information is fabricated by shadowy conspirators.