The re-emergence of Russia as a military power and its action in Crimea and Syria has radically changed the US-Russian relationship.
After years of increased co-operation, e.g. through the NATO-Russia Council and with Russian membership of the G8 Group, the US was of the view that Russia was no longer the threat to European peace and security it once was.
Russian President Vladimir Putin’s actions in supporting the anti-government rebels in Ukraine have resulted in extensive US and European economic sanctions being imposed on Russia.
The US has become frustrated with Russia over Syria.
The on-going civil war in Syria has led to the loss of thousands of lives, while millions have been displaced.
Russia has supported President Assad through the conflict. It launched an air campaign to support his forces in 2015. This turned the war in the government's favour.
Russia has also supported the Syrian government by means of its UN Security Council veto. This has meant the US has been unable to gain UN approval for action. For example, the missile strikes carried out by the USA, UK and France in April 2018, in response to chemical weaopn attacks, was carried out without UN approval.