American politicians and the Russia-North Korea alliance

There have been multiple reports in the news about Russia and North Korea strengthening their alliance, leading to 

North Korea sending military supplies to Russia, and in return 

Russia supplying technological assistance to help North Korea develop its weapons program yet further.

Is this good for the United States?

Of course not.

What caused Russia to enter into such a close relation with North Korea?

It is a reaction to the actions the U.S. has taken against Russia, over the Russia-Ukraine war.

And why did the U.S. take those actions?

Because the U.S., specifically U.S. politicians, cannot acknowledge the legitimacy of Russia's concerns that led at its attack on Ukraine that started in February 2022.

See John Mearsheimer, 

"Why is Ukraine the West's Fault?", 2015, 75 minutes

https://youtu.be/JrMiSQAGOS4

And why do American politicians so support Ukraine?

Well of course one factor is surely because that is what elite media is telling them they should do.

But I suspect there is another, more significant to them, reason:

Because that is what their campaign donors want them to do.