PH I agree with you. I actually think the Progressive Party would have to rise out of minority heavy (and safe Dem) districts, which is why "The Squad" and other progressives of color excite me. All you need to do is have a popular incumbent progressive congressperson run for reelection as a member of the Progressive Party. They have the name recognition to get by without the D next to their name and all you need is for that party to gain 5 or 6 Congressional seats and our current corrupt two-party system gets turned on its head.
Grow that number to 15-20 House seats over time, maybe a Senate seat or two, and the Progressive Party becomes king maker. The Democratic Party will have no choice but to move left and work with the Progressive Party in order to get anything accomplished. The Progressive Party can choose to back the Democratic presidential nominee or not.
On the flip side the Democratic Party would probably gain disaffected fiscal conservatives who can't don't associate themselves with nativism, but also don't want to pay a humane tax rate. A win, win for everyone except the racists.