A Democratic congressman said President Donald Trump’s key campaign promise of building a wall along the U.S.-Mexico border would be a “monumental waste of taxpayers’ money,” but Democrats should go along with it if necessary to win Republican agreement for granting legal immigration status to 'dreamers.'

“I think the wall is a monumental waste of taxpayer money, and it’s to build a monument to stupidity and it’s just idiotic,” Rep. Luis Gutierrez, D-Ill., told ABC News Chief Anchor George Stephanopoulos on "This Week" Sunday.

PHOTO: President Donald Trump speaks at the Conversations with the Women of America event at the Eisenhower Executive Office Building on the White House complex, Jan. 16, 2018. Manuel Balce Ceneta/AP
President Donald Trump speaks at the Conversations with the Women of America event at the Eisenhower Executive Office Building on the White House complex, Jan. 16, 2018.

“Having said that, if that’s what it’s going to take in order to put 800,000 young men and women in the country, 'dreamers,' ... in a safe place and put them on course to full integration in our society ... I say pay it,” Gutierrez said.

Stephanopoulos noted that Trump promised during his election campaign that Mexico would pay for the border wall "Twenty billion dollars that Mexico was supposed to pay?"

"That's exactly the point, $20 billion," Gutierrez responded.

Mexico has insisted it will not help cover the cost for a wall.

But, Gutierrez said the president has said he wants a wall, "and, as despicable as it is, as hurtful as it is to people like me and others in this country, we are ready to sacrifice that so that dreamers can have freedom in this country."

Stephanopoulos noted that White House Legislative Affairs Director Marc Short said in his appearance on "This Week" Sunday that funding the border wall would not be enough and that there also need to be changes in two practices that enable legal immigration -- the visa lottery system and chain immigration.

"Are you willing to accept that?" Stephanopoulos asked.

Gutierrez said the administration keeps moving the goal post because its true goal is to end legal immigration.

"Here's what they're saying to us, George, and we have to be very clear about it, and we are going to fight this: They want to end legal immigration to the United States," the congressman said. "They say, 'Let's build a wall to keep us safe. But then ... they say, ‘The lottery system, let's end it.' That's legal immigration to the United States."