With just over 60 days left in office, Joe Biden’s White House has significantly escalated the Ukraine war it had tried so hard to contain by authorising the use of US-supplied medium-range ATACMS (Army Tactical Missile Systems) and antipersonnel mines against targets inside Russia. Biden’s U-turn breaks a long-standing convention on US presidential transitions that lame-duck presidents aren’t supposed to make major foreign policy changes – especially not ones that severely constrain the stated policies of their elected successor.