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As the fight continues over President Trump’s demand to extend the border wall between the United States and Mexico, one thing is clear: Whatever the wall’s effect on immigration might be, it would have an impact on the environment of the borderlands.

About 650 miles of border wall already exist along the 2,000-mile boundary between the two countries. Most of it has been built on federal land where the terrain provides no natural barrier. Mr. Trump has called for a 1,000-mile wall, which would extend farther across land that includes important habitats for wildlife.

A Customs and Border Protection policy says the agency “will integrate environmental stewardship and sustainability practices into operations and activities.” But Congress has given the agency the power to waive environmental protections like the Endangered Species Act. Such laws could require the government to produce an in-depth environmental impact analysis of a new project, develop less-damaging alternatives and perform environmental monitoring after construction.

A spokesman for Customs and Border Protection was unavailable because of the partial government shutdown, a result of the political standoff over funding for the wall.