We don't really know what it would be like to have Bernie in office, because he wasn't popular enough to get there. But I could imagine it would be hard for him, yes, because no one wants him to be President.
There is bottom up pressure. Clearly. Self-evidently. There could be more if people who don't want the Republicans in power actually made any kind of effort politically, rather than complained on Lemmy about unsubstantiated conspiracy theories that a cabal of spooky capitalists subvert the Democratic process so your vote doesn't matter.
The Dems are in power because they won the election, solely because more people voted for them than the Republicans. If you VOTE, you effect change.