Cankle's poll numbers were horrid. She had an ice cubes chance.
Look for the birther story to be made public as soon as old crazy Joe gets sent packing into retirement. That moves her to the #2 slot.
I further think that Obama may have had as much dirt on Bill and Hillary as they had on him. Remember, Rahm Emanuel was a Clinton insider, and Chicago politics thrives on desroying the opposition,
I think Biden is Obama's firewall. Whatever Congress thinks of Obama, they know that Biden will be an unmitigated disaster. It would be like appointing the class clown as a substitute teacher.
Back in the 70's, Spiro Agnew was in a similar position. Nixon wanted to get replace him for the '72 re-election campaign, but decided to keep him on. John Ehrlichman claimed that he asked Nixon why he kept Agnew on the ticket in the 1972 election, and Nixon replied that "No assassin in his right mind would kill me."
Congress couldn't get rid of Nixon and let Agnew take his place. The US Attorney provided them the opportunity, by charging Agnew with accepting bribes 5 years earlier while Governor of Maryland. He plead guilty to a single charge of tax evasion (not reporting the bribery income), under a deal where he resigned as Vice President.
So, I think you are right: Joe is the canary in the coal mine. When he suddenly finds himself between a rock and a hard place and is forced to resign, Obama will be next.