Who is a lame duck?

Senator John Kyl and Representative West are lame ducks.  Scott Brown is a lame duck.  President Obama is not a lame duck.

The second and third definitions in Merriam Webster are relevant here.

2: an elected official or group continuing to hold political office during the period between the election and the inauguration of a successor
3: one whose position or term of office will soon end
Since President Obama is neither of these, it is wrong to call him a lame duck and assume therefore has no power to act.  He won’t reach lame duckness until after the 2016 election.
But we are in the midst of a lame duck session of Congress and we are trusting them to solve our fiscal crisis which they were unable to do the last two years.  Good luck to us all!