Extending Russia, Rand Corporation 2019

The United States could also become more vocal in its support for NATO membership for Ukraine... While NATO’s requirement for unanimity makes it unlikely that Ukraine could gain membership in the foreseeable future, Washington’s pushing this possibility could boost Ukrainian resolve while leading Russia to redouble its efforts to forestall such a development.

Expanding U.S. assistance to Ukraine, including lethal military assistance, would likely increase the costs to Russia, in both blood and treasure, of holding the Donbass region. More Russian aid to the separatists and an additional Russian troop presence would likely be required, leading to larger expenditures, equipment losses, and Russian casualties. The latter could become quite controversial at home, as it did when the Soviets invaded Afghanistan.

https://www.rand.org/content/dam/rand/pubs/research_reports/RR3000/RR3063/RAND_RR3063.pdf

Not currently

Not that we know of, it’s possible they are getting there though.

Afaik they, as a principle, do not have nukes but retain the capability to manufacture them. Probably a good one since having nukes makes them a target of America and not having nukes also makes them a target of America and others. Every soverign state looks at what president nobel peace prize did to Libya as a reminder of what happens to states that denuclearize.

Iran is not threatening the USA in any meaningful way.

On the other hand, USA is constantly invading the middle east, promoting genocide and terrorism, and literally trying to nuke Iran.