I searched for this quote. I read articles about any speeches/talks she gave on June 18 2020. No record of anything like this. There is a Politifact (leftist site of course) that supposed fact checks stuff.
Harris has said enough stuff without having to pass along made up quotes, it certainly seems like something she thinks and plans and would say. I’ve seen many quotes attributed to varius famous figures, Thomas Jefferson in particular, and apparently there is a cottage industry of making up fake quotes. There is actually a website dedicated to finding out quotes from Thomas Jefferson to determine authenticity, I’ve visited it quite a few times.
In this case, it looks as though Politifact is correct, excerpt:
A quote from Sen. Kamala Harris attacking supporters of President Donald Trump has been widely shared on social media. But it’s made-up.
The quote, which was published Oct. 29 and Nov. 2 on Facebook, makes it look like Harris, a Democratic senator running for president in 2020, threatened people who voted for Trump in 2016.
The quote reads: “And once he’s gone and we have regained our rightful place in the White House, look out if you supported him and endorsed his actions, because we’ll be coming for you next. You will feel the vengeance of a nation. No stone will be left unturned as we seek you out in every corner of this great nation. For it is you who have betrayed us.”
Oops- copied link twice instead of content:
Daniel Funke
By Daniel Funke
November 4, 2019
Kamala Harris didn’t say Democrats are ‘coming for’ Trump supporters in 2020
A quote from Sen. Kamala Harris attacking supporters of President Donald Trump has been widely shared on social media. But it’s made-up.
The quote, which was published Oct. 29 and Nov. 2 on Facebook, makes it look like Harris, a Democratic senator running for president in 2020, threatened people who voted for Trump in 2016.