I am slowly making my way through Delaware's State Senate elections. The State Senate has been elected to staggered terms ever since it was first established in 1776, and they have been screwing it up since 1832.
Up until 1898, three senators were elected from each county. Originally, they were elected to three-year terms, one elected from each county every year. This is the only valid way to have staggered terms for your legislature. However, Delaware changed to having elections on even years only in 1832, and as such changed senatorial terms to four years, one-third elected on presidential election years and two-thirds elected on off years. Michael J. Dubin says in his book that half were elected every two years. This is objectively wrong.
In 1898, senatorial districts were implemented and the size of the legislature was increased to 17. Seven of these seats were elected on presidential election years, and ten on off-years. Delaware went on to not redistrict until the Supreme Court gave all the states an intervention in the lead-up to the 1964 election. This is why, in 1954, the first district of New Castle had nearly 25,000 votes, while the seventh district had less than two thousand. Which brings us to the subject of this map.
The Republicans had controlled the Senate since the 1928 election. During the 30s and 40s, the political system shifted so that the 10 midterm districts mostly tended to vote Republican, while the 7 main year districts tended to vote Democratic. Eventually, however, in 1950, the Democrats managed to get a 9-8 majority, but this was lost in 1952, when the Republicans won 3 out of the 7 districts up for election that year, bringing them to a 10-7 majority.
Then, in 1954, the Democrats managed to win eight of the ten seats up for election that year (with 51% of the vote), giving them a 12-5 majority. In 1956, due to the Republicans not fielding a candidate in New Castle's 2nd district (the first time since 1878 that there had not been a Republican candidate in any district), it was mathematically impossible for them to regain control over the Senate. Instead, they lost a seat, bringing the Democratic majority up to 13-4. The Democrats won about 59.5% of the vote in 1956. There were no known third-party candidates in either election.