I'm no fan of Pres. Trump (didn't vote and will never vote for him) but the "cages" were built during the previous administration: https://www.apnews.com/fdfbafe1f2784a759bc7c3a8e8ddbcab (also see here: https://qz.com/1291470/photos-immigrant-children-detained-at-the-placement-center-in-2014/). The current president makes a number of egregious claims about immigration but those cages were built and used during Pres. Obama's administration.
When they where built is irrelevant. What is relevant is that they are being used now and how they are being used. Any person who can cobble together a rational thought can see that immigration enforcement has changed significantly while Trump has been president.