Speaker of the House Nancy Pelosi and Senate Minority Leader Chuck Schumer said President Trump's national emergency declaration does "great violence" to the US Constitution.
In a joint statement, they said the so-called crisis at the border that Trump described "does not exist."
"This is plainly a power grab by a disappointed President, who has gone outside the bounds of the law to try to get what he failed to achieve in the constitutional legislative process."
They urged their Republican colleagues to fight against the declaration.
"Just as both parties honored our oath to protect the American people by passing the conference committee bill, the Congress on a bipartisan basis must honor the Constitution by defending our system of checks and balances," they said. "The President is not above the law. The Congress cannot let the President shred the Constitution,"
Here's their full statement: