Or he's a pragmatist who is concerned with both harm reduction and the likely reality that the only takeaway that Democrats will ever have from losing an election to someone right wing is that Democrats need to go even further to the right to win.
If leftists give the impression that nothing will ever be good enough for them then
- Democrats have no incentive to court the left
- Democrats have no estimate for how many votes they would even be able to pick up from the left relative to how far left they might try to reach
I personally believe that if the Democrats had taken on a progressive populist anti-genocide platform they would have won the election handsomely, but I am left with no way to empirically prove that to anyone because so many leftists opt out of voting entirely.
The "reform is impossible" is a self-fulfilling prophesy because it leads leftists to never try to get involved in the party, which means they'll never get a seat at the table, which means they'll never be able to steer the party.
I certainly can't prove that the influence of big money can ever be overcome within the party by grassroots organization, but you also can't prove that it's impossible (you can only prove that it's difficult, which is something I certainly won't dispute).
You certainly can't prove that a true socialist movement will ever gain traction in America. It seems like the general public is so brainwashed they would rather be indentured servants of large corporations than lift a single finger to seize the means of production.
So we're left with two unprovable paths to consider, and here's the thing: the two paths are not mutually exclusive. Leftists can try both at the same time with neither being disruptive to the other. So this is the pragmatism: consider all possibilities and put the eggs into more than one basket.