On an economic level, from ~1860 to ~1925 the two were roughly even, but after this the Democrats became markedly more economically liberal. On social issues, the switch happened on a presidential level from ~1964 to ~1984, but took some time to percolate down ballot. As a result, it would be accurate to say the GOP during much of the 19th and 20th centuries was the more “liberal” party. Nowadays, this is clearly not true.
How many GOP nominees from 1896-1996 was more liberal than the Democratic one lol(There is only 1 and that is 1904)
The fact is ever since the election of 1896 the GOP has been the more conservative party, and the election of 1912 solidified it.
I wonder if TR had won the GOP nomination in 1912 instead of running third party, if that would have taken the party in a progressive direction for the foreseeable future.