Twitter hides Donald Trump tweet for “glorifying violence”

Twitter is well within the rights to do this, but I have seen tweets from blue check marks essentially calling for violence and Twitter didn't remove them. So, does that mean Twitter actually -supports- those view points now? If Twitter is going to police people, it needs to be across the board. Otherwise it's just a weird censorship that is targeting one person and can easily be seen as political.

Everyone is applauding this because they hate Trump, but take a step back and see the bigger picture. This could backfire in serious ways, and it plays to Trump's base's narrative that the mainstream media and tech giants are colluding to silence conservatives (and maybe there could even be some truth to that.) I know the Valley is an echo chamber, so obviously no one is going to ever realize this.

The valley being an echo chamber doesn’t necessarily mean those implementing this have their heads in the sand.

It can’t be all perfectly achieved, but to do nothing, as they were before, could be now determined to be a worse case than providing these annotations to flagrant misuse by the highest impact profile that they can’t do away with entirely.

The issue is that the rules are being enforced selectively. Just this week Twitter fact checked Trump's opinion on mail voter fraud by linking to other experts' opinions. It seems more like a move to influence the election rather than enforcing the rules.

Selective enforcement happens everywhere in the internet. For example if you go to T_D in Reddit, they will absolutely delete any anti-Trump posts. Does this mean Reddit is influencing elections ?

Opinions that particular subreddit and its moderators aside, that's not really about a site enforcing a policy selectively. Moderators are usually volunteers, and as far as I know, Reddit doesn't have a policy saying they should be neutral. As long as they do stuff that is within the bounds of Reddit's policies, moderators can be pretty arbitrary or capricious.