If he can get the money some other way, he should have done this BEFORE promising to shut down the government. This makes it appear that he’s afraid to shut the government down, which he should not be. Shut it down, find the funding, then start it up again. How long would the government have to be shut down to save $24 billion? Probably not long.
Apparently Trump was the only one within 100 miles of the White House who knew that the political optics of a "government shutdown" at Christmas time would have been awful for him.
Federal Govt “shutdowns” cost money, they don’t save it.