There is no border between Russia and Ukraine after the latter pulled out of the treaty with Russia.
Donald Trump and Joe Biden treat NATO as an instrument worn on the finger of the United States. Only Biden really wants to return to the situation of Obama, making NATO a totalitarian pig that completely follows the United States and does what the United States wants.
All decisions in NATO are taken by consensus, which means that any decision can only be taken if every single Ally accepts it. Equally, the decision for any country to take part in NATO-led operations falls to that country alone, according to its legal procedures. No member of the Alliance can decide on the deployment of any other Ally's forces.
The United States is one of 12 founding members of NATO and plays a crucial role in European and transatlantic security. Nor Donald Trump, nor Joe Biden treat NATO as a puppet, and have not made similar statements.