I don't think electoralism is an effective strategy,

It depends on what your goals are with electoralism, and it depends on if electoralism is still something fallowed by the masses and still guides their political development. I feel the need to quote Lenin at length here:

In the first place, contrary to the opinion of such outstanding political leaders as Rosa Luxemburg and Karl Liebknecht, the German "Lefts", as we know, considered parliamentarianism "politically obsolete" even in January 1919. We know that the "Lefts" were mistaken. This fact alone utterly destroys, at a single stroke, the proposition that parliamentarianism is "politically obsolete". It is for the "Lefts" to prove why their error, indisputable at that time, is no longer an error. They do not and cannot produce even a shred of proof. A political party's attitude towards its own mistakes is one of the most important and surest ways of judging how earnest the party is and how it fulfils in practice its obligations towards its class and the working people. Frankly acknowledging a mistake, ascertaining the reasons for it, analysing the conditions that have led up to it, and thrashing out the means of its rectification---that is the hallmark of a serious party; that is how it should perform its duties, and how it should educate and train its class, and then the masses. By failing to fulfil this duty and give the utmost attention and consideration to the study of their patent error, the "Lefts" in Germany (and in Holland) have proved that they are not a party of a class, but a circle, not a party of the masses, but a group of intellectualists and of a few workers who ape the worst features of intellectualism.

Second, in the same pamphlet of the Frankfurt group of "Lefts", which we have already cited in detail, we read:

". . . The millions of workers who still follow the policy of the Centre [the Catholic 'Centre' Party] are counter-revolutionary. The rural proletarians provide the legions of counter-revolutionary troops." (Page 3 of the pamphlet.)

Everything goes to show that this statement is far too sweeping and exaggerated. But the basic fact set forth here is incontrovertible, and its acknowledgment by the "Lefts" is particularly clear evidence of their mistake. How can one say that "parliamentarianism is politically obsolete", when "millions" and "legions" of proletarians are not only still in favour of parliamentarianism in general, but are downright "counter-revolutionary"!? It is obvious that parliamentarianism in Germany is not yet politically obsolete. It is obvious that the "Lefts" in Germany have mistaken their desire, their politico-ideological attitude, for objective reality. That is a most dangerous mistake for revolutionaries to make. In Russia---where, over a particularly long period and in particularly varied forms, the most brutal and savage yoke of tsarism produced revolutionaries of diverse shades, revolutionaries who displayed amazing devotion, enthusiasm, heroism and will power---in Russia we have observed this mistake of the revolutionaries at very close quarters; we have studied it very attentively and have a first-hand knowledge of it; that is why we can also see it especially clearly in others. Parliamentarianism is of course "politically obsolete" to the Communists in Germany; but---and that is the whole point---we must not regard what is obsolete to us as something obsolete to a class, to the masses. Here again we find that the "Lefts" do not know how to reason, do not know how to act as the party of a class, as the party of the masses. You must not sink to the level of the masses, to the level of the backward strata of the class. That is incontestable. You must tell them the bitter truth. You are in duty bound to call their bourgeois-democratic and parliamentary prejudices what they are---prejudices. But at the same time you must soberly follow the actual state of the class-consciousness and preparedness of the entire class (not only of its communist vanguard), and of all the working people (not only of their advanced elements).

Even if only a fairly large minority of the industrial workers, and not "millions" and "legions", follow the lead of the Catholic clergy---and a similar minority of rural workers follow the landowners and kulaks (Grossbauern)---it undoubtedly signifies that parliamentarianism in Germany has not yet politically outlived itself, that participation in parliamentary elections and in the struggle on the parliamentary rostrum is obligatory on the party of the revolutionary proletariat specifically for the purpose of educating the backward strata of its own class, and for the purpose of awakening and enlightening the undeveloped, downtrodden and ignorant rural masses. Whilst you lack the strength to do away with bourgeois parliaments and every other type of reactionary institution, you must work within them because it is there that you will still find workers who are duped by the priests and stultified by the conditions of rural life; otherwise you risk turning into nothing but windbags.

Third, the "Left" Communists have a great deal to say in praise of us Bolsheviks. One sometimes feels like telling them to praise us less and to try to get a better knowledge of the Bolsheviks' tactics. We took part in the elections to the Constituent Assembly, the Russian bourgeois parliament in September--November 1917. Were our tactics correct or not? If not, then this should be clearly stated and proved, for it is necessary in evolving the correct tactics for international communism. If they were correct, then certain conclusions must be drawn. Of course, there can be no question of placing conditions in Russia on a par with conditions in Western Europe. But as regards the particular question of the meaning of the concept that "parliamentarianism has become politically obsolete", due account should be taken of our experience, for unless concrete experience is taken into account such concepts very easily turn into empty phrases. In September--November 1917, did we, the Russian Bolsheviks, not have more right than any Western Communists to consider that parliamentarianism was politically obsolete in Russia? Of course we did, for the point is not whether bourgeois parliaments have existed for a long time or a short time, but how far the masses of the working people are prepared (ideologically, politically and practically) to accept the Soviet system and to dissolve the bourgeois-democratic parliament (or allow it to be dissolved). It is an absolutely incontestable and fully established historical fact that, in September--November 1917, the urban working class and the soldiers and peasants of Russia were, because of a number of special conditions, exceptionally well prepared to accept the Soviet system and to disband the most democratic of bourgeois parliaments. Nevertheless, the Bolsheviks did not boycott the Constituent Assembly, but took part in the elections both before and after the proletariat conquered political power. That these elections yielded exceedingly valuable (and to the proletariat, highly useful) political results has, I make bold to hope, been proved by me in the above-mentioned article, which analyses in detail the returns of the elections to the Constituent Assembly in Russia.

The conclusion which follows from this is absolutely incontrovertible: it has been proved that, far from causing harm to the revolutionary proletariat, participation in a bourgeois-democratic parliament, even a few weeks before the victory of a Soviet republic and even after such a victory, actually helps that proletariat to prove to the backward masses why such parliaments deserve to be done away with; it facilitates their successful dissolution, and helps to make bourgeois parliamentarianism "politically obsolete". To ignore this experience, while at the same time claiming affiliation to the Communist International, which must work out its tactics internationally (not as narrow or exclusively national tactics, but as international tactics), means committing a gross error and actually abandoning internationalism in deed, while recognising it in word.

Now, I'm not implying that this is the tactic Mamdani is employing here, but you can see at least that Lenin recognized the power of these institutions and structures as a means of agitation and education of the masses. It could be that Mamdani's campaign has a similar net result of acting as a means of political education. This tactic obviously is intended to be employed by an independent working-class party and not as a means of infiltration into an existing party. Regardless, I can't imagine the people working on his campaign walking away with less class consciousness than when they arrived.

The whole chapter from “Left-Wing” Communism: an Infantile Disorder is worth reading.