Stein’s and the Green Party’s behavior in the 2016 election is quite suspicious.
People often think of the Green party as the left’s equivelant to the Libertarian party. But that’s not a good comparison. Whatever you think of the Libertarian Party, they’re a real political party. They stay active all the time. They run candidates from the local level through the presidential level and honestly do their best to win.
The Green Party is not really a political party in the same way. They don’t run local or state candidates. They basically go dormant between presidential elections. Their party, such as it is, is basically just a token formality to let them run a presidential candidate every 4 years.
They seem to exist not to promote a real party with a real agenda, like the Libertarian party attempts to do, but to play the spoiler in presidential elections.
Now - you could say that maybe they just want to get on the national stage and spread their message. But Jill Stein didn’t campaign widely as someone who wanted to promote a leftist message. One goal of third party presidential candidates is to get enough of the vote to get federal funding in the next election and be invited to presidential debates. This is actually probably their #1 practical goal they might achieve.
So if Jill Stein was a well-meaning leftist who wanted to try to promote her party to get her message out, you would expect her to campaign in places like California, where people might feel like they can safely “throw their vote away” on a third party because Clinton would definitely win. Relatively easy votes for the picking, and it doesn’t hurt your ideology as much because you aren’t as likely to play as big a spoiler, thereby letting the Republicans win (which you should, as a leftist, oppose far more than the democrats).
But what did Jill Stein actually do? She campaigned in swing states. That amplified the potential spoiler effect (boosting the chance of Republicans winning that election) while also minimizing the votes for her own party relative to a place where people could safely vote Green Party. That’s exactly the wrong strategy to use if you were promoting a leftist agenda. But exactly the right strategy you would use if you were trying hard to play the spoiler so Republicans could win.
Combine this with the fact that the Russians meddled in our elections in multiple vectors, and Stein has no particular businesses at a dinner with Putin and Manafort, and the fact that she still tries to promote Trump, which is antithetical to any sort of leftist, and her behavior is extremely suspicious.
I think the most plain reading of this situation is that she’s working to undermine the democratic party in presidential elections and may be receiving from Russia to do so.