Another email:

To clarify what your emailer said (“In the 1930 off-year elections, the Democrats came within 2 votes of a majority in the House (218 Republican/216 Democratic)”), I’d note the following. First, there was a Farmer-Labor congressman elected, so it was more like 218-217. Second, the Republicans lost their majority in 1931 before they could use it. Recall that this was before the 20th Amendment passed, and Congress didn’t convene for the first time until about 13 months after the election, unless there was a special session. In 1930, a whole heap of Republican representatives died between the election and the session, and the Republicans did horribly in the special elections, so that when Congress finally convened, the Democrats actually had the majority in the House. (In the Senate, the GOP held it 48-47, with 1 F-L guy making it 48-48.)

If you’re looking for past elections that might prove helpful in understanding the next one, I’d suggest skipping 1930 (and 1994) in favor of 1942 and 1966.