The barriers currently at the three sites block vehicles from passing but still allow wildlife to move through. Environmental groups said the 9.1-metre replacement bollards that the Trump administration plans to erect would prevent the cross-border migration of wildlife.

Said the creator of the GoFundMe raising funds for the wall, "I've been receiving thousands of emails from citizens who have waited in line to become Americans and completed this process the legal way."

Trump said he marveled at the Flight 93 National Memorial during a visit last week.