Bill De Blasio:

I think it's a tragedy that doesn't have to be in America.

I think this happened for a reason. It's the proliferation of weapons and the ease with which people can get them. And now it is this additional horrible reality of white supremacy growing in this country, this movement of white supremacy growing, aided and abetted by messages from the White House.

We have to understand, this wasn't the case 20 years ago. We have seen these mass shootings become more and more common, and on top of it now more often coming with a political agenda. We saw that with the Tree of Life Synagogue in Pittsburgh. We saw that in Poway, California, now El Paso.

We have to understand something's changed. And I think we have to confront it two ways. One, Congress needs to come back and pass some commonsense gun laws, background checks, the basics, a waiting period before you get a gun, get rid of assault weapons.

But, second, we need leadership that's actually going to unify us and not tear us apart.