Washington (CNN) President Donald Trump has become increasingly sensitive to criticism that he's backing off his signature promise to build a wall along the US-Mexico border, three sources familiar with his concern tell CNN, as aides fear the administration's chances for securing funding for it have sunset.

GOP lawmakers and Trump are set to OK a short-term funding measure to avert a year-end government shutdown and Democrats will assume control of the House in 2019, virtually assuring no additional border wall funding.

Trump's anxiety about fulfilling his top campaign goal comes at the end of months of bitter debate inside the West Wing over how to fund the border wall between those seen as ideologues and those who consider themselves pragmatists.

White House officials were in a meeting discussing border security last August when a sudden outburst from aide Stephen Miller silenced the room. The President's legislative affairs director, Shahira Knight, was in the middle of arguing that instead of pushing for the border fight so close to the midterm elections, the White House should hold off until after November when they would be in stronger position to fight over funding.

Miller, the immigration hardliner at the table, cut her off mid-sentence. According to two people in the room, he shot back with a list of reasons why the administration would almost certainly be in a weaker position after the elections because Republicans were guaranteed to lose multiple seats and possibly the entire House, making building the wall all but impossible.

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