After all the alliances and arithmetic, the party is likely to ________ a majority in the assembly election.

The sentence in question talks about election arithmetic and political alliances. Here, the phrase "after all..." suggests a limited result. The verb phrase that is needed in the blank should convey the idea of merely obtaining a majority, or a victory that is not comfortable.

Option B: "scrape together" is ideal in this situation, as the phrase means "to gather something with difficulty", which is appropriate given the precarious political majority.

The other choices don't feel quite right. Option A, "scrape through," refers to barely passing, an exam for instance , not forming a majority. Option C, "tape together," refers to repairing broken items, which is not relevant in this situation. Option D, "shape together," is not an idiom.

Thus, Option B is the right choice.