Allusion to a line in Trump's speech, early in his presidency, at the CIA - he referenced a '5th column' and that it is/going to be removed.
In a 2017 speech to the CIA, President Trump mentioned……COLUMNS
"I will tell you, final time, although I will say it, when you let in your thousands of other people that have been trying to come in, because I am coming back – we’re going to have to get you a larger room. (Applause.) We may have to get you a larger room. You know? And maybe, maybe, it will be built by somebody that knows how to build, and we won’t have COLUMNS. (Laughter.) You understand that? (Applause.) We get rid of the COLUMNS."