Only since Putin openly said in 2006 that Russia's nuclear arsenal was the only way for the world to stop "US aggression", Born.
Bush's war in Iraq and the supposed pretexts that created it was a wake up call for Putin. He was sure we were heading after his buddy Assad, the head of the other Baathist regime next door, that had a operating chemical weapons program built for them by the Soviets decades before, next. That imperiled the then small Russian Naval facility on the Mediterranean Coast of Syria. It was and is their only true warm water refueling port in the Med with access to the Atlantic year round could go with Assad, which was intolerable to the Russians. Murmansk, the only other outlet to the Atlantic that is semi-open year round is above the Arctic Circle and often has to be kept open by nuclear power icebreakers, is woefully inadequate and was major hindrance during the even the glory days of Soviet Union. They've got Vladivostok, but that's next to North Korea.
What has been the centerpiece of Russia's foreign policy since the time of Peter The Great? Access to warm water ports. Control of the Bosporus, entrance to the Black Sea is key to that.. What's stopped them from trying that for nearly the past 70 years? Turkey's membership in NATO as Turkey sits on both sides of the straits. Throw in Greece, another longstanding NATO member with the Turks, and NATO owns the Aegean Sea and access to the Med from those straits What was the key to post WWII Soviet, and now Putin's foreign policy? Breaking NATO to accomplish that primary goal. The main powers in the West will absolutely go to war over a Russian push towards the Bosporus, NATO or no NATO.
What is Putin's stated personal goal for Russian foreign policy in his lifetime? To restore Russia as closely to it's Soviet borders and military status. That means goodbye to the Baltic States, all NATO members, the Ukraine, Belarus, Moldova, a chunk of Romania, all of the states in the Caucus region north of the Turkish border, and the Central Asian "Stans" except for Afghanistan, where they, the British before them and finally ourselves have awakened to the fact it's better to let the Afghans keep it.
The initial grab of Crimea? The port of Odessa which only sees mild icing in the winter. The current war in the Ukraine? To restore Russia's breadbasket and "Holy Kiev" home of the first Rus state and birthplace of the Russian Orthodox Church. These are issues with very deep roots.
Iran along with it's proxy Hezbollah have been working shoulder to shoulder with the Russians to prop up Bashar Assad, the Gas Man of Syria, in a civil war that has raged since late 2011. Without their interference that war would have likely been done in 2013, and Bashar on trial in the Hague. Instead Putin raised the specter of his nuclear arsenal when it looked as if the we were going to intervene, thus the war wages on. (I've never forgiven Obama for not calling his bluff on that one.) Bashar Assad, Putin's friend since since his days as a young KGB officer in Lebanon assisting Syria and allied forces there in the Lebanese Civil Wars, is sitting pretty in Damascus today with all the eggs in his basket.
Finally the Russians assisted the Iranians in starting up their nuke program in the 90's, destabilizing not only the Middle East but adding the possibility of another nuclear power cheek to jowl with both Pakistan and India in South Asia, a traditional tinder box. When did Russian assistance in that begin in earnest? When Putin took power. You see, the Straits of Hormuz have been a goal of the Russians since the time of the Czars, too. A permanent Russian naval base there would be disaster of epic proportions, giving the Russians control of not only their own oil and gas reserves, but that of the Gulf States and Iran, and a base of operations in the Indian Ocean. Who would control the tap on oil then?
This is a huge geopolitical moment and the current POTUS is woefully inept, lacking the mental toughness needed to do the job at hand, and very possibly too compromised by the role the Russians played in the election to have the sack to do anything about it.
Any other questions about "When did the Russians become the enemy?"
Don't underestimate Putin, he's a brilliant and totally ruthless autocrat. He had nearly thirty years of training before he reached the top of pile in an environment where the slightest mistake could cost you and your family their lives. He's not some Wall Street/corporate exec or real estate mogul that's had a cushy life, with the only great risk since adulthood being losing other people's money and missing out on dinner reservations.