For example, let’s say Bernie Sanders was the nominee in 2024 against Trump. A lot of people on the internet seem to like him, even some conservatives. But would liberals fall in line and vote for him enough to beat Trump?
Bernie’s supporters always seem to attack the Democrats liberal base, do you think they’d sit home if Bernie or any leftist was the nominee.
In the context of Germany, “liberal” means being for capitalism unbridled by the state but still generally progressive policies culturally, with more rights for minorities and such. The corresponding party is FDP. So in some ways it’s the exact opposite of the US idea of “liberal”.
Someone considered “left” would be for more social policies and government control of capitalism (traditionally SPD), extreme left would be following tenants of communism, opposed to the US and friendly with Russia (The party The Left and the new Sarah Wagenknecht party)
Someone considered conservative or “right” would be against social policies and try to reduce control of capitalism (CDU) extreme right would be plain fascists (AfD), ironically also aligned with Russia now.
The Greens are a special case, since they were originally a single issue party concerned with environmentalism, but since the SPD has largely vacated their social policies since Schröder was chancellor, they have become more and more the new “social” party.
There are also a huge number of smaller parties that are unable to reach more than five percent, which is necessary to be included in the govenmental body of the Bundestag. Most of those are single issue parties (there is even a beer party). The FDP has become so unpopular that it might also share that fate soon.
To come back to your original point, there were no “liberals” when Hitler was elected. There were conservatives, socialists and communists. The conservatives aligned themselves with the fascists and the socialists and communists were outlawed and thrown into jail/executed.