The son of former President Ronald Reagan issued a warning to President Trump last week, advising him to build his long-proposed border wall.

Michael Reagan tweeted at the president, saying that "it's now or never" and that he must "#BuildTheWallNow."

Reagan noted his father's Immigration Reform and Control Act of 1986, which granted legal status to millions of immigrants and also penalized employers for hiring those without legal work permits.

"My father is still waiting," Michael Reagan tweeted.

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On "Fox & Friends" on Monday, George Rodriguez -- a former special assistant during Reagan's administration -- said that the 40th president would tell Trump to "be very, very careful."

"Everybody was talking about [that] we've got to do an amnesty because enforcement was going to be too much," he said. "We need to put some sugar into the legislation, so to speak. Well, it turns out here we are, 2018, and the only thing that we've got is diabetes from all that sugar and we never got the enforcement that we really needed."

Rodriguez recommended Trump circle back to Reagan's act from 1986 and enforce it.

"You've got a lot of undocumented folks that are taking advantage of federal benefits that they shouldn't be. This is a magnet that brings these people and keeps them here," he said.

President Reagan would have supported constructing a border wall, he said, adding that the flow of undocumented immigrants into the U.S. is "out of control."

"The border has always been open and has always had problems with illegal immigration, but not like it’s got it today," Rodriguez said. "I know that he would say 'do something.'"

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