I think the phrase is backwards
If you support the Democrats you are not a leftist, you are not progressive, you are Trump with a blue coat of paint.
rather:
If you're leftist/progressive, why are you supporting these policies, or supporting the politicians who support these policies? Where do you stand on immigrant rights? Did you dislike when trump did x y z? Obama created those border cages first, and was known as "deporter-in-chief" among immigrant rights groups and socialists for being so draconian. Then, with Kamala as "Border-czar," Biden deregulated the border camps, allowed them to be privatized, and issued an executive order to totally shut the border which when Trump tried to do it it was so extreme the courts blocked him on multiple separate levels.
Then you're getting positive engagement, actually having them tell you what they believe and having conversations about it, and challenging the politicians to pull the worker away from hollow faith in jackals.
Rather than just accusing people of things, calling them names, and acting in a gatekeeping way pushing them further from ever accepting leftist positions because you're actively telling them that they don't and aren't leftists and basically insulting them and condescending to them for being misled by the agents of empire who have total media and social media narrative supremacy. which might make you feel good but does nothing to convince anyone and does nothing to grow socialism.