The White House is not shutting down chatter of a potentially calamitous government shutdown.

President Donald Trump is "serious" about his government shutdown threat, a senior administration official told NBC News Thursday, marking an escalation from the commander-in-chief’s warning earlier this week.

On Tuesday night, at a campaign rally in Phoenix, Trump threatened a shutdown if his wall along the Mexico border isn’t funded by Congress, telling the crowd, "If we have to close down our government, we're building that wall."

"We're going to have our wall. The American people voted for immigration control. We're going to get that wall," Trump said to cheers of "Build the wall! Build the wall!"

The Trump administration official told NBC News that such a showdown with Congress, over funding for construction of the border wall, could come in September when lawmakers return from their August break or after the passage of a short-term spending bill in December.

A Sept. 30 deadline is approaching to continue funding the government. If Congress failed to pass a funding resolution, the government would shut down.

Trump aide Kellyanne Conway echoed her boss, telling Fox News on Thursday morning that Trump was "steadfastly committed" to building the wall, and that he expects the funding to do it.

"Anybody who’s surprised by that has not been paying attention for over two years," Conway said. "So he’s telling Congress he’s building the wall, he expects the funding, and it’s up to them to work collaboratively. We hope they do."

Trump himself amped up his attacks on GOP leaders in Congress on Thursday, charging that they had ignored his instructions on debt ceiling.

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