Trump wants to use his declaration to steer US$3.6 billion more than Congress has approved for building border barrier.
Senators Lamar Alexander of Tennessee and Mitt Romney of Utah became the sixth and seventh Republicans to say they'd vote for a resolution to annul the emergency Trump declared last month.
Just four defections would ensure the measure would be sent to the White House, where Trump has promised a veto. There is no indication that opponents of his declaration have the required two-thirds majority in both houses to overturn a veto.
"I'll do a veto. It's not going to be overturned," Trump said. "It's a border security vote."
Many lawmakers from both parties consider the declaration of an emergency to be a dubious and dangerous expansion of presidential authority.
Democrats, set to oppose him, say there is no emergency at the border. They argue Trump issued his declaration because Congress only agreed to provide less than $1.4 billion for the barriers, and he is desperate to fulfil his campaign promise to "Build the Wall". (AP)