If you don't get the most votes you will not have to worry about "selling out", you will be out.
I'm a gay, socialist, leveler who believes, roughly, in the Quaker idea that each person has a spark of the divine in them and that they have inherent, absolute rights which they must exercise in full recognition of the rights of every other person. I could go into my leftist credentials further but I think you would agree this puts me on the far left side of things.
Nancy Pelosi is, beyond any dispute, the person farthest on the left to have held leadership in the House, the Senate or the executive, there is no evidence that anyone farther to the left is going to achieve power during our life times. Some individual members of congress are to her left, though not that many, arguably one or two of the senators, other than dear Senator Sanders, might be to her left. When we are talking about national office, the universe of what constitutes "the left" is not the same as that when we are talking about those of us who have either been unable or unwilling to achieve election to a public office*. We, old chum, are not going to constitute the governing left any time in our life times. For us, assuming you're roughly in my age cohort, when we are talking about national office, considering our "left" is a waste of time.
I'd rather have a more progressive tax code and a reduced carbon load in the atmosphere in the foreseeable future than in arguing about what will not be.
And, I assure you, a politician who has to win an election will have to deal with the much larger constituencies who aren't as far left as we are, in any case.
I'm done with pretending that unachievable principles are worth sacrificing the possible. That "ideal" isn't an ideal, it's a feel-good pose. It will feed no children, provide no one with health care or preserve one hectare of land or ocean. All of which are more important than any abstract ideal I happen to hold.
* Volunteering in a political campaign, seeing what they go through, I’m sick and tired of hearing people run down our politicians. They are just about all dedicated to pubic service. Few moderate to liberal Democrats serving in elective office at the national level couldn’t be enjoying a much more comfortable and profitable life pursuing a wealth-making career. With considerably fewer headaches. You think it’s such a bed of roses, try getting yourself elected. Try dodging the bullets and balancing the pressure groups. Anyone who wonders why they ignore people acting like crybabies should stop wondering. Acting like a crybaby is you inviting them to ignore you. They have to.