Congressman John Culbertson of Texas came back to Twitter after an extended absence to say he might stick around, assuming the site's problems with trolls and spammers have been taken care of. That was back in August and he hasn't followed up on it, so we must assume that trolls and spammers are still in full effect on the site.
Most politicians probably come into office dreaming of changing the world, but real politics often involves nitty-gritty focus on details that seem trivial to most of us but are important to some constituents. Senator Susan Collins of Maine, for instance, has been thinking about nothing since the beginning of November but the regulation of heavy trucks on interstate highways, or at least that's the impression you'd get from her Twitter feed.
Other politicians use their Twitters to reveal their obsessions outside the political realm. Senator Chuck Grassley of Iowa, for instance, likes collegiate volleyball. He really, really likes it. Everyone needs a hobby, I guess.