U.S President Donald Trump set off a Christmas social media storm when he asked whether a 7-year-old was too old to believe in Santa Claus, capping a week of plunging stocks, a government shutdown and the U.S. defense chief's unceremonious departure.

Twitter lit up like a Christmas tree after Trump made his remark during a holiday event with first lady Melania Trump, taking calls from children calling the North American Aerospace Defense Command Santa tracker.

A Christmas tradition, the tracker delights children with "real-time" updates on Saint Nick's Christmas Eve journey.

In one of the Christmas Eve calls, Trump chatted with a 7-year-old.

"Are you still a believer in Santa?" Trump asked the child. "Because at 7, it's marginal, right?"

In a twinkling, Twitter was bombarded with messages railing against the president for what sounded to some as if he was casting doubts on a cherished fantasy of childhood.

"It’s just too freaking fantastic that Trump spent his Christmas Eve calling seven year olds and telling them believing in Santa at their age is 'marginal,'" Democratic Senator Chris Murphy said on his Twitter account.

“Actually there is no heaven," tweeted Dan Amira, head writer for "The Daily Show with Trevor Noah" comedy show. "When you die you just rot in the ground and get eaten by worms. Okay Merry Christmas, Timmy.”

Others defended Trump.

"Trump does a lot of things wrong, but suggesting to a 7 year old that Santa doesn't exist is probably the one right thing he's done while in office," said a man identified on his Twitter account as Irtiza Sheikh. "Someone's gotta do it."

The White House had no immediate comment on the social media response to the president's Santa comments.

In 2017, Trump spent the holidays at his Florida estate, Mar-a-Lago, with his family, but for his second Christmas as president, Trump opted to cancel his holiday getaway because of the partial federal government shutdown. It began last week when top lawmakers failed to end an impasse over funding for his proposed wall along the border with Mexico.

Stuck in Washington on Christmas morning 2018, Trump displayed little holiday cheer while speaking with reporters after a 20-minute video conference with U.S. troops serving abroad.

He assailed the Federal Reserve for raising interest rates, railed against Democrats who refuse to fund the wall he wants to build on the U.S.-Mexico border, and blasted the investigation into his campaign's ties to Russia, among other regular targets.

The president then closed with holiday wishes of sorts.

"It's a disgrace, what's happening in our country," he said. "But other than that, I wish everyone a very merry Christmas."