President Donald Trump is expected to lay out plans Wednesday to speed up construction of his promised wall along the Mexican border. But while he can make some moves on his own and possibly start construction, finishing the wall will require a big assist from Congress.

That’s what USA Today writes in this explanation about what the new president will need to make good on his campaign promise. Some fencing and walls already exist. But to build an additional 1,200 miles, he would need funding from Congress. Republican leaders have not committed to funding but said they would help Trump secure the border.