I think the phrase down the rabbit hole is actually referring to Alice in Wonderland. But.
I would say the organism that tends to burrow the deepest into the Earth is humans. Average oil well depth appears to be around 5,964 feet (1818 meters), that’s pretty deep. The deepest hole we ever drilled is supposedly the Kola Superdeep Borehole dug by the Soviets, it was 40,230 feet (12.2km) deep.
Perhaps not answer your looking for though.
https://www.npr.org/2022/11/11/1135878576/the-democrats-strategy-of-boosting-far-right-candidates-seems-to-have-worked
The TLDR; Democrats raised money for far right candidates during their primaries in some strategic elections, the idea being that given the choice between a sane moderate democrat and a lunatic maga republican in the general election, people would choose the sane option.
I don’t know that is what’s happening here however, even if they threw a massive amount of money at Robert F. Kennedy Jr it seems unlikely he would ever win the democratic presidential primary.