Matt Yglesias has a piece titled Against Murder-Suicide Politics where he criticizes the left for threatening or actually withholding electoral support from Democrats who do not pursue their desired policies.
Yglesias starts the piece by establishing what he thinks is normal and productive behavior within a political coalition by pointing to how the right-wing of the Republican party operates, which he says is by providing electoral support without requiring that candidates tout their issues on the hope that they will get their issues dealt with when Republicans win.
Then he contrasts that with the way the left-wing of the Democratic party operates, which is suggesting or threatening to withhold electoral support unless candidates tout their issues and pursue them when they are in office, which he compares to murder-suicide.
I’ve thought a lot about this question over the years and I’ve found most people’s approach to it lacking, primarily because their view on what constitutes a normal and productive baseline for coalition politics is way off the mark.
To my mind, the normal and productive way to do coalition politics is for the various factions in the coalition to first acknowledge that they disagree on certain things but that it is nevertheless beneficial to work together in order to control the government. From there, the various factions ought to receive policy dispensations that are proportional to their size.
Thus, a small left-wing faction in coalition with a large center-left faction may be allowed to pass a policy or two and get one cabinet position even though the center-left faction may not support the policy or the appointee. In exchange, the left-wing faction will agree to pass the policies and support the appointees of the large center-left faction even though the left-wing faction may not support those policies or the appointees.
You see this kind of arrangement a lot in multi-party democracies during government formation.
Something like this occasionally happens in the US, but not generally. Instead, the general expectation among Democrats at least seems to be that the left should support the appointees and policies of the center-left regardless of the relative sizes of the two factions and that what the left should get in return for that is the avoidance of right-wing governance. Even if a policy is supported by the majority of the Democratic party, including the Democratic elected representatives, it is seen as perfectly normal for even a very small number of moderate Democrats to veto it, so long as that number is enough to prevent a majority.
This bizarre situation where a handful of center-left moderates engage in this kind of hostage-taking and the punditry does not view it as insane and outrageous seems to be caused by a variety of factors, including that there are only two major nominal parties, that the parties are weak, and that we have a tricameral lawmaking process that frustrates the kinds of unified government formation you see elsewhere in the world.
But I don’t think you can understand why the left threatens electoral support without fully appreciating the problems created by a world where the center-left’s understanding of the proper role of the left is to provide endless confidence and supply rather than to share in the power.
I wrote something similar to this back in 2015 in a post titled “What is the left supposed to do electorally?” In that post, I mused about the fact that the center-left accuses the left of behaving recklessly no matter what it does in elections. If the left runs as a separate party, this is characterized as reckless vote-splitting. If the left runs in party primaries and wins, this is characterized as recklessly risking general election electability. But if you can’t run as a third party or run in the primary, then what are you supposed to do?
The answer of course is the same as above: support the center-left even as the center-left’s position is that it can and should reject everything you want to do. Not only should you not push the center-left on its policy positions, but you also should not challenge them in elections. Just provide the confidence and supply.
Needless to say, this is not a very effective way to approach someone who you want to partner with. The center-left is very good at spinning up stories about how the wacky left is acting in a wacky way, but very bad at seeing how their approach to working with the left is repulsive and wacky in its own way.
As noted already, I think the theoretical way you solve this problem is through power-sharing where the left is given a certain dispensation over policy and personnel that is commensurate with its size. In a world where the left could trust that this would happen, it probably would focus more on growing its voter base and turning them out for the Democratic party and less on threatening to withhold votes. But for as long as the center-left’s attitude is that it should be allowed to govern however it wants rather than share power proportionally, many on the left will not see the point of cooperation.