A Reddit thread.
Where the line is drawn - not taking corporate PAC money. Rich individuals can contribute. If they lean toward Our Revolution and/or Justice Democrat policy, that might incline them to contribute; whereas the Koch brothers likely gave zippo to Ro. Organized union money? That might have an answer, but none is known to Crabgrass. The prevailing terminology "no corporate PAC funding is accepted."
Now if Michele PAC were to offer Khanna a contribution, would that be accepted? Clearly a hypothetical. Does Michele PAC give to anyone besides Bachmann lawyers, these days, if ever?
Is Michele PAC still alive and accepting money? Seems so, given that PAC accepting it in 2016.
UPDATE: Campaign spending is a part of things. Apart from campaigns, there also are the independent (allegedly independent at least) slush funds [can you say Norm Coleman] which collect and spend lavishly, primarily on the Republican side but also some for corporatist Dems to work to tamp down progressives.
However, the hope is there is less a direct dependence/indebtedness in practice (as well as a formal fig-leaf), when the money stays out of the campaign coffers.
Money corrupting politics by corrupting politicians; or by helping the already corrupt ones; is the problem. The nation's supreme court [deserving lower case for this] are the ones who green-lighted the spending of the green, more is merrier, and if you want to criticize and hate on anyone