“And with our sister state partners, we are ready to go,” he told ABC’s “This Week.”
“We’re confident there are at least 8 billion ways that we can prove harm.”
Other Democrat-controlled states are expected to join the action and House Democrats have said they will introduce a resolution that would block the declaration.
Ultimately, the legal battle will probably end at the conservative-leaning Supreme Court to which Mr Trump has appointed two justices since he took office.
Stephen Miller, a senior White House adviser, told Fox News on Sunday that the declaration would allow the administration to build “hundreds of miles” of border wall by September 2020.
“We have 120-odd miles that are already under construction or are already obligated plus the additional funds we have and then we’re going to outlay – we’re going to look at a few hundred miles.”
He also suggested the US leader would veto Congress should there be any resolution to block the emergency declaration.
“Obviously the president is going to protect his national emergency declaration.
“This (illegal immigration) is a threat in our country … and if the president can’t defend this country, then he cannot fulfill his constitutional oath of office,” he added.