It's up to the current members to decide who can join and who can't. That should also include considerations of opportunity.
> Russia has been messing with Ukraine politics since the collapse of the USSR. Why shouldn't US be allowed to?
The US is allowed to do whatever its military and economic power allows it to. Then actions have consequences. The consequences had been stated clearly.
> pretty much not doing anything when Russia attacked Georgia, occupied Crimea
Here, check the history of sanctions of the EU to Russia. It goes back to 2014.
https://www.consilium.europa.eu/en/policies/sanctions-agains...
And as history showed, they did the right choice. Or war in Ukraine would be war in Ukraine + Baltics + Romania.
> The US is allowed to do whatever its military and economic power allows it to. Then actions have consequences. The consequences had been stated clearly.
So US is messing with Ukraine, which Russia doesn't like, therefore Russia attacks Ukraine, because it can't compete using its whip with the Wests cookie. Logic checks out.
> Here, check the history of sanctions of the EU to Russia. It goes back to 2014.
So pretty much ignored Russian invasion of Georgia in 2008. The only sanctions Russia understands is boots on the ground and rockets (now drones) attacking their military and refineries.