Because it would send the NRA over the edge and give them a bully-pulpit from which to preach that Dear Leader and the Democratic Party would never live down.
It would also expose to many middle class and uncommitted voters the degree to which the Administration is willing to influence public opinion behind the scenes.
It would not go well for Dear Leader or the Dem's in the Nov elections.
So basically Chris Matthews (according to what you’re saying) is right and this is political and not really to seek justice for the deaths of the border agents and hundreds of Mexicans including women and children? Do the family members appearing at the committees know this?