I do not consider the answers steadfastly or ensure that I put in a variable effort and every one of my answers does not interrelate with each other. Hence, if you find my answers wrong, just consider it this way that I haven’t looked at the final answer and I cannot know what the final answer will be. I am just using my basic skills to make sure that I put in the right effort.
At the first blank, my prediction or choice is ‘benefitted by’. And there are some basic reasons for this. First, I think the talk is about the majority party in an election and thus its representation in the legislature. And if you consider any majority party, there will be more seats for it and thus there will be a favorable situation for it. Thus, if you look for the word ‘benefitted by’, it shows that the majority party will find it feasible in the seats.
For the second blank, I am going with seismic. It was a difficult decision to consider this option since it was difficult to select from the ones. Seismic seems of diverse changes and thus if you look at majority, the second extreme is minority and hence I think seismic option suits and sits well.
The final blank allows me to go for culpable since it means guilty or something that is wrong. If I consider other options, they seem to be either polite or pointing to the extreme and I cannot think of a better option that sits well with the condition that the question is pointing towards.

The correct words for the blanks are (i) dispossessed of, (ii) seismic, and (iii) culpable.

Breakdown of the Blanks
- Blank (i): A. dispossessed of

The sentence describes a "longstanding pattern" where the majority party loses seats in the election after a presidential win. The phrase dispossessed of means to be deprived of or to lose. This fits the context of a party losing legislative seats.
- Blank (ii): F. seismic

The sentence states that this pattern is "more to do with nonpartisan practicality than with (ii) $\qquad$ shifts in political ideology." This sets up a contrast. The shifts in ideology are not the cause; something else is. Seismic means of enormous proportions or effect. In this context, it refers to a massive, fundamental change in political beliefs. The sentence argues that the cause is not these huge ideological shifts, but rather a more mundane, practical reason.
- Blank (iii): G. culpable

The final blank explains the "nonpartisan practicality." Voters are described as weary of problems and they "usually find... the party in control." The word culpable means deserving of blame. Voters, feeling weary of problems, typically blame the party that is in power. This is the "nonpartisan practicality" that the sentence refers to.

The Complete Sentence
"The longstanding pattern in which the majority party is dispossessed of a large number of legislative seats in the election cycle after winning the presidency has more to do with nonpartisan practicality than with seismic shifts in political ideology. Voters inevitably weary of the problems that afflict society at even the best of times, and they usually find culpable the party in control."