The X post in question is indeed authentic; the official @KamalaHarris X account originally published it on April 21, 2017, as part of a longer thread on the topic of immigration and citizenship. The full thread is as follows:

An undocumented immigrant is not a criminal.

Give people a path to citizenship. The vast majority of folks we’re talking about are living a lawful life and paying taxes.

It’s ludicrous to say we’re going to deport 12 million people. Now how are you going to do that?

We are not a society that is going to stand for tearing families apart. We are not going to buy into this administration’s fear mongering.