See, earlier Pelosi: "The Fact Is, a Wall Is an Immorality. It's Not Who We Are as a Nation."

From iSteve commenter Ty Rade:

Could be a throwback, warped in translation, to Samuel P Huntington’s last book in 2004, ‘Who are we?’ In which he mapped the void that is being left by the overthrow of the dominant white-anglo- saxon glue that has held America together thus far. I’d suggest there is no ‘we’ in ‘it’s not who we are’ at all; and that’s the trouble.

From iSteve commenter Coag:

Saying “This is not who we are” aims to push emotional buttons of shame and guilt, and as a meme is simple, memorable, and infectious. Trump, and all nationalists, should therefore appropriate it and use the phrase incessantly, just like how he appropriated the term “fake news”.

Leaving our front yard wide open and our loved ones undefended from drug smuggling and migrant caravans? That is not who we are.

Allowing illegal immigrants to undercut our fellow American citizens’ wages and livelihoods? That is not who we are as a nation.

Giving lavish attention and prizes to illegal immigrants while neglecting the well-being of our suffering urban and rural areas? That is not who we are.