Expanded from an earlier answer of mine,

The political structure of the USSR was an incredibly complex and filled with contradictions. Although the Marxism celebrated a scientific and rational view of the world, power within the USSR was often nebulous and capricious. For instance, there was no clear mechanism within the Soviet state for succession in the executive leadership, so Kremlinologists and other interested parties would watch the funeral procession to see who would succeed the departed. Much of the way the USSR was run operated contrary to the lines of power the three Soviet constitutions outlined in 1924, 1936, and 1977. While the Soviets had many of the trappings of a democratic system, it was far from a democracy in any meaningful sense of the word.

One of inescapable realities of political life in the USSR was that the Communist Party (CP) was one of the central organs of power. Article 6 of the 1977 constitution formally claimed the CP to be:

The leading and guiding force of the Soviet society and the nucleus of its political system, of all state organizations and public organizations, is the Communist Party of the Soviet Union. The CPSU exists for the people and serves the people.

The Communist Party, armed with Marxism-Leninism, determines the general perspectives of the development of society and the course of the home and foreign policy of the USSR, directs the great constructive work of the Soviet people, and imparts a planned, systematic and theoretically substantiated character to their struggle for the victory of communism.

All party organizations shall function within the framework of the Constitution of the USSR.

Yet for all of these paeans to the CP, its actual delineated role within Soviet politics was unclear. Article 6 itself was a break from the two prior constitutions that did not specifically claim the CP was the central political lodestone.

The general phrase developed by political scientists during the Cold War to explain the Soviet system was that the Party ruled, but did not govern. What this means is that the CP formed a sort of parallel power structure that was deeply intertwined with other state entities. CP membership became one of the means of promotion within the system and an important box to tick off for any Soviet citizen aspiring to rise up through the system. However, CP membership in itself was not formally a requirement for institutions and not all CP members were elites. Particularly as the system evolved in the post-Stalin years, there were other interest blocs that developed within the Soviet state. The regional chiefs within Gosplan (the agency tasked with central economic planning) were more than likely CP members, but they were more beholden to their own fiefdoms than the Party bureaucracy. The influence of the CP varied from department to department and how high up one was in the pecking order for certain agencies. In the latter case, the local CP might have been powerful for low-level managers and executives, but its direct power decreased higher up the chain of command. These competing interest blocs often formed alliances in the Party Congress elections to the CP's Central Committee- which was a gateway to the Politburo/Presidium of the CP. These CP elections were not elections per se, but rather a process in which the end result was known even before the ballots were cast by the CP's elite delegates.

This all leads to the question of elections. Soviet elections were very complicated entities, even during the period after Stalin's death. Although it was a one-party state and a highly authoritarian one at that, the Stalin Constitution of 1936 made both provisions for free elections and the Stalinist state staked a good deal of its legitimacy upon high turn-out during elections. The Stalin Constitution remained in force until 1977, when Brezhnev ordered a new constitution which was a document much like its predecessor.

Most Soviet citizens had to vote for delegates to the Supreme Soviet, the major parliamentary body in the USSR. Although both the 1936 and 1977 constitutions imbued the Supreme Soviet with broad, sweeping powers, the reality was quite different. The Supreme Soviet appointed the members of the Presidium of the Supreme Soviet, which was nominally the executive branch of the Soviet state. In practice, the Supreme Soviet and its Presidium were toothless rubber stamps for the choices of the executive leadership of the Politburo. In keeping with the nebulous nature of Soviet power, choices for the Presidium were often fait accomplis for the Supreme Soviet to approve without much deliberation.

The various Soviet constitutions allowed candidates from outside the Communist Party to stand for elections to the Supreme Soviet, but they usually had to be nominated or approved by their local CP apparatus. There were detailed guidelines from Moscow about acceptable candidates and the state forbid adversarial or negative electioneering campaigns. More often than not, voters usually had a choice from a single candidate, especially after the 1977 constitution. Elections were called by the Presidium of the Supreme Soviet at regular scheduled intervals and took place in districts designated by the state.

This system led to an aspersion in the West that Soviet elections were "elections without choice," and there is a great deal of truth in this charge. However, this charge can obscure the inordinate degree of attention on Soviet regime lavished upon elections. The Stalin Constitution nominally provided for a secret ballot and a degree of candidates and the state used high electoral turnout to legitimize the grand Soviet experiment. The 1977 constitution also decreed an election's results to be invalid if turn out was low. High turnout was also a means of social control by the state as elections verified that the voter was a legal resident of a particular area. Therefore, local officials were often under intense pressure to guarantee a high political turnout for both propaganda and practical purposes. This was one of the reasons why voter turnout in the USSR typically averaged in the eightieth percentile from 1937 onward and the numbers are probably quite accurate.

While many local CP officials fudged the numbers of turnout, this was a dangerous stratagem for the apparatchik if caught. Like some political bosses in the West, these local officials preferred to employ various inducements over obvious chicanery to get voters to the polls. From the Second World War onward, Soviet elections increasingly assumed a holiday-like atmosphere to attract voters. Similarly, mobile voting booths were often used to make sure that infirm voters could cast their ballots. The intense pressure from the center on these local officials to deliver the numbers gave the Soviet voter leverage in which abstaining from voting gave the voter a degree of power. Voting against a candidate, such as scratching out the name, was an embarrassment to the local CP officials and detrimental to their careers. The various meetings in the run-up for Soviet elections were often a time when the public could petition the officials for local improvements, repair of infrastructure, and airing other grievances. There was also a pronounced uptick in petitions and other requests to the electoral officials and newspapers during election season and some of these entreaties included the threat that if they were not met by election day, these individuals would boycott the election. By the same token, some Soviet voters would sometimes write petitions on the ballots to the authorities. Some of these preserved ballots have patriotic slogans, but others contained personal requests or denunciations of local officials.

Although Soviet elections were not democratic in any formal meaning of the word, they were an anemic channel for political communication between the state and its citizens. Over the long-term, these "elections without choice," did foster an apathy over the Soviet system and its many hypocrisies, but they did also provide a mechanism to cope with the grim reality of a single-party state. Even without any real electoral choice, many Soviet citizens recognized that there was some degree of power in the act of voting and bargained with local officials accordingly.

Sources

Jessen, Ralph, and Hedwig Richter. Voting for Hitler and Stalin: Elections Under 20th Century Dictatorships. Frankfurt: Campus Verlag, 2011.

Sakwa, Richard. Soviet Politics in Perspective. London: Routledge, 1998