"Purity Tests" is the term corporate Democrats use when people ask them about money they take from big donors and how it influences their policies.

Lots of great facial expressions from multiple people in that photo

It's a standard corporate dem response, these days, to complain about "purity tests." It's not a purity test when we demand an official stand against corporate greed. The regressive taxes, targeting the poor, is not the way to get our city out of our current crisis.

Purity tests often refer to activists who demand perfect anti-corporate records before we should support them

Taking the holier-than-thou, moral high-ground piss has always been a distinguishing characteristic of extreme ideologues at both ends of the spectrum. You can agree with them 95% of the time, but someone is always going to hold up that 5% (or 3% or 1%) difference as demonstrating your lack of sufficient dedication to the cause; and in their mind that picayune variance makes you virtually indistinguishable from those directly in opposition to their espoused values and beliefs.

"Democrats should refocus on delivering a strong message to people living in rural areas, he says."
That explains what Murray's doing--because he's sure not sending a useful message to the people of this urban area.