A spew of satirical "Missing" posters with de Blasio's image recently began cropping up all over the city; when asked if he agreed if de Blasio was "the missing mayor" as the posters allege, Trump replied: "I think that speaks for itself."
De Blasio was elected mayor in 2013, replacing Republican billionaire Michael Bloomberg and thus becoming the first Democrat to hold the position since 1989; he went on to be re-elected in 2017.
Back in 2016, when his father was still the Republican nominee for president, Trump Jr. was asked about running against de Blasio, and said "if I could do that as a service to my country, I would love to do that."
He didn't; and since the job is a two-term maximum, his only option now would be to succeed him, rather than defeat him at the polls. Even as recently as May of this year, a New York Post report claimed he was considering a run for Mayor.
There has never been much love lost between de Blasio, a former Hilary Clinton campaign manager, and the Trump family. De Blasio has previously referred to the President as "Con Don", while Trump described him as "the worst mayor in the history of New York City."
Indeed when de Blasio announced he was stepping out of the race for the Democratic nomination last week, Trump had a cynical tweet waiting.
"Oh no, really big political news, perhaps the biggest story in years! Part time Mayor of New York City, @BilldeBlasio, who was polling at a solid ZERO but had tremendous room for growth, has shocking dropped out of the Presidential race," he tweeted. "NYC is devastated, he's coming home!"
Another former NYC Mayor, Rudy Giuliani, currently serves as the President's personal lawyer.