There's two things wrong with this statement. Obama hasn't been shifting his position on Iraq, but also... he's already right smack in the middle of American public opinion.
Here's some recent polling:
"If you had to choose, would you rather see the next president keep the same number of troops in Iraq that are currently stationed there, or would you rather see the next president remove most U.S. troops in Iraq within a few months of taking office?"
Keep Same Number: 33%
Remove Most: 64%
"Do you believe that the United States should bring most of the troops home from Iraq in the next year or two, or should the U.S. wait until Iraq is relatively stable, even if it takes four years or more?"
In the next year or two: 56%
Wait Until Stable: 39%
"In your opinion, should the United States withdraw troops from Iraq right away, or should the U.S. begin bringing troops home within the next year, or should troops stay in Iraq for as long as it takes to win the war?"
Withdraw Right Away: 25%
Withdraw Within a Year: 43%
Stay as Long as it Takes: 26%
The conservatives critics of Obama who label him a political opportunist for allegedly changing his position have got it wrong; if he were to do so, he would either be an electoral dunce or a paragon of political courage.