Relationships between US and Russia deteriorated

Putin feels threatened by NATO's expansion said that this move is going to ignite a new arms race similar to the first Cold War. Bush's reply defended the plan, stating that the missiles are intended to protect Europe from possible attacks from Iran and North Korea (isn't North Korea a little far though?). However, Putin made it clear that the missile plan is more threatening to Russia than to Iran or North Korea, considering that Iran does not have the missiles America intends to shoot down.
In conclusion, we are about to enter an era where world leaders have to compensate by showing who has the biggest missile.