He's building a case. Nancy and Chuckles wouldn't go to the border, so he's bringing the border to them in the form of public hearings. Let the Border Patrol and ICE present public testimony about the effectiveness of a wall, and let the Dems ignore it. Makes presenting his case of a national emergency that much stronger. Of course, Dems can present their own witnesses who will testify that walls are ineffective. I'm sure they'll be persuasive. (Sarcasm)
Pelosi and Schumer can only play their childish game of ignore, with their fingers in their ears--or up their asses--for only so long.
OTOH, I was so f'ing wrong about Comey's motives that I'm probably FOS about this, as well.
