They think they can somehow impeach both Trump AND Pence (claiming Pence was in on it, or perhaps the alphabet-soup lobby that despises Pence so much can gin up some other charge against him) and furthermore somehow negotiate a settlement with Congress forcing Pence to nominate Hillary as his successor.
Or, plan B, win both House and Senate in 2018, then impeach Trump and Pence before Pence can nominate a VP, and install President Nancy Pelosi.
Both are pipe dreams.
Yeah, that is nutty fantasy talk. But, Democrats live in a fantasy-world anyway, so they have the ability to believe anything. (illegals do not commit crimes, 71 genders, for example) Maybe it is a scam? Maybe the guy wants to take advantage of Liberal lunatics by fundraising for his cause.
Immediately following the election, many Libs were thinking of the election like baseball game or a boxing match. They really did believe that if they could get Trump impeached that Hillary would then "win by default", so to speak. To any rational person, this idea was Liberal Lunacy. To the Liberals, it was their last shot to save America and the World from total destruction.
At least now they have come to realize that getting rid of Trump will do little or nothing for them. But they still want to do it anyway, just for revenge.
Even if they get rid of Trump and Pence, then we have President Ryan. Their impeachment plan simply cannot work, no matter what they do. They are setting themselves up for failure.