I really don't understand how the RATs accomplished that on the congressional level since we are not a parliamentary system and the vote for Congress wasn't tied to the vote for President.
In order to similarly split the vote at the congressional level, the "Progressive Party" (a new third party created solely for Teddy Roosevelt's egotistical Presidential run, it wasn't related to previous "Progressive Party" campaigns in the U.S.) would have to slate candidates aligned to Teddy's ideals in each of the 435 congressional districts. Furthermore, the quality of the candidates themselves would ALSO have to mirror the presidential choices... if you had an extremely popular incumbent Republican congressman up for re-election against a weak Dem and a no-name, underfunded "Progressive" candidate, its unlikely the Progressive candidate would get the same % of people who pulled the lever for Teddy to do the same for him, and its very likely the Republican candidate for Congress would outperform Taft at the top of the ticket. Also, in 1912, there were numerous areas of the country that were 1 party Republican and simply never had any RATs on ballot (ironically, most of those places, like Vermont, are now safe Dem)
If anything, I would have assumed the Republicans did well in Congressional races in 1912 because they're usually straight Republican vs. Democrat races, and most Wilson voters would vote RAT, while most Taft voters and a plurality of Teddy voters would pick the "R" over the "D" in a two way race.
In short, I'm shocked the RATS did so well on the congressional level.
I don’t know many total candidates they ran but the Progs got 13% of the total vote according to Wikipedia, (winning just 10 seats), GOP 35% , rats 43% (several points less than they got in 1910 when they just edged the GOP in popular vote yet won a good majority of seats), and the Socialists over 6% (slightly outpolling the Debs Presidential Ticket).
The Progressive vote was almost entirely out of the GOP hide, and it was more than enough to screw us, it doesn’t take a lot.
This was long before ticket splitting became in vogue, incumbents personal popularity was not a major factor back then, people voted party. We’re lucky the majority of TR votes stuck with the GOP on the Congressional level, if the split in Congressional vote was the same as in the POTUS race 27% prog, 23% GOP, the rats would have won an even huger majority, maybe around 80%, like Wilson got in the electoral college.
The UK may see Labour win a decent majority with well under 40% of the vote thanks to the Tory/UKIP split.