PRESIDENT Donald Trump is facing legal challenges to his decision to use emergency powers to build a wall on the US border with Mexico.

The top two Democrats in Congress said they would use “every remedy available” to oppose what they cast as an unlawful measure.

Trump announced he was using emergency measure to secure more money for his long-promised wall on Friday, using an interpretation of his presidential powers that was condemned as unconstitutional.

In his emergency proclamation, Trump claimed the border was “a major entry point for criminals, gang members, and illicit narcotics” and one that threatens “core national security interests”. Illegal border crossings are down from a high of 1.6 million in 2000.

Trump signed the declaration to justify diverting billions of federal dollars from military construction and other purposes after Congress approved only a fraction of the money he had demanded.

Within hours, the first legal challenge –made by the American Civil Liberties Union (ACLU) – against the declaration of national emergency was launched.

The stand-off over border funding had led to the longest government shutdown in history. To avoid another Trump reluctantly signed a funding Bill on Friday which included just $1.4 billion of the $5.7bn he had demanded for the wall.

“Sadly, we’ll be sued and sadly it will go through a process and happily we’ll win, I think,” he said at a news conference where he also claimed this was an attempt to make the process “faster” .

ACLU executive director Anthony Romero, said: “By the president’s very own admission, there is no national emergency. He just grew impatient and frustrated with Congress, and decided to move along his promise for a border wall ‘faster’.”

Some Democratic state attorneys general have also threatened to go to court over the decision. A liberal advocacy group, Public Citizen, sued on behalf of a nature reserve and three Texas landowners who have been told the wall may be constructed on their properties.