California Lt. Gov. Gavin Newsom (D) compared President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE to "Pennywise," the killer clown in Stephen King's novel and movie "It."

The California gubernatorial candidate tweeted the response after the president took aim at Newsom's support for progressive immigration policies at a rally in Las Vegas, Nevada earlier in the evening.

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"lol, hi @realDonaldTrump," Newsom tweeted Thursday. "Interesting description coming from the guy who is literally locking up kids like Pennywise."

Newsom's tweet referred to the Trump administration's ongoing detention of minors who were brought to the U.S. illegally by their parents across the U.S. border with Mexico. Current numbers from the administration count the number of detained children at more than 12,000.

lol, hi @realDonaldTrump.



Interesting description coming from the guy who is literally locking up kids like Pennywise. pic.twitter.com/bt49kyGk9Z — Gavin Newsom (@GavinNewsom) September 21, 2018

Trump insulted Newsom as a "clown" who supported "open borders" at his Nevada rally earlier on Thursday.

“Democrats want to give welfare and free health care to illegal aliens,” Trump said. “How about this clown in California who’s running for governor? He wants open borders and then he wants to give them health care, education, everything.”

Newsom is facing Republican John Cox in the state's gubernatorial election after surviving a field of nearly 30 candidates in the June primary.

A RealClearPolitics average of polls shows Newsom with a more than 20-point lead over his Republican challenger.