True, though the circumstances there were fairly unique - there was a major underlying realignment in the GOP’s favor in the South going on at that time and the economy was coming back out of the dot com bust (Bush was lucky that his term started largely at the nadir of that). This alt-1918 would be/will be more similar to OTL’s demob elections that went against the recently-triumphant governments
So let's take a peek at 1918 then.
Going in we had a slim Democratic House (218-215) and bigger Democratic Senate (54-42). Afterwards we had GOP control of both houses (240-192 and 49-47). So what caused that? Demobilization? The war itself was still ongoing. Over a million Americans were still fighting in the Meuse-Argonne campaign for example. There were probably two million American servicemen in France in late 1918.
So I don't particularily buy "demobilization" as an excuse for 1918. The 1946 US and 1945 UK elections - sure. But we're talking about 1918.
So what caused the 1918 elections. First of all, while a GOP victory, we're hardly talking a wave. The non-Presidential party wining 25 seats in the house and 6 in the senate. In 1914, the GOP won 62 seats. In 1910, Democrats won 55 seats. In 1906, Democrats won 32 seats. 25 seats is well within the margins there. [1]
We have three reasons why the GOP won seats in 1918.
1 - The normal election cycle of early 20th Century midterms as shown above, especially in the House
2 - Wilson's own popularity. He raised taxes to pay for the war and yet still had to borrow a ton - leading to a wonderful combo of high taxes
and inflation.
3. Wilson fragmenting the Democratic Party. His own abrasive personality and and pissed off German-Americans (formerly a huge Democratic constituency) depressed turnout in traditional Democratic strongholds such as the Midwest and major cities.
So what's different here ITTL. Much of this is pure speculation but I'm drawing off what the OP has previously mentioned. Let's look at each of my three above points and talk about them
1 - Midterm Cycles: Midterms in this TL more or less follow the same "Party that's not in power gets seats." Looking from 1886-1906 you have the following elections where the out-of-power party gains seats in the House: 1886, 1890, 1894, 1898, 1902, 1906. Wait a second...
that's every single midterm! So it is safe to say that the general midterm rules apply here as well. That would bode well for the Democrats right? Well...
2 - Presidential Popularity: Instead of the prissy and staid Wilson, loathed by a major constituency and hated by tons of power brokers in his own party, we have Charlemagne Hughes running the show, victor of the Great American War. This timeline's sources so far have treated Hughes as wise, charismatic, and lucky. Who's to say that won't hold - especially when combined with what the OP has called the "Liberal Quadradecennium," an essentially unprecedented era of one-party dominance not seen since before the Civil War.
3 - Party Fragmentation: I can't answer any questions about how/if any political parties fragment or what happens on the ground as that stuff hasn't been posted yet 🤷♂️
The question thus is the following: Is Charlemagne Hughes, shown up to here so far in the TL as stacking wins on top of wins on top of wins, combined with the OP's previous statements of 1880-1920 being a Liberal era/wank, enough to offset what has been as predictable as the tides - losing parties win the next midterm (at least in the House)[2]
[1] If you average out the opposing party seat gains in the 1906, 1910, 1914, and 1918 midterm elections, you get 43.5 seats won by the non-Presidential party in those four elections.
[2] I purposely didn't look at the Senate as ITTL and OTL there wasn't direct election of Senators until the early 20th Century.