War-time presidents and lost popularity

From ABC:

If there’s a shadow over the proceedings as Barack Obama addresses the nation on his plans for Afghanistan tonight, it may be the ghosts of wartime presidents past.

Consider the chart below. The data track the average annual approval ratings of the last three presidents to find themselves enmeshed in unpopular wars. The picture is not a pretty one: Harry S. Truman lost 25 points in public approval as the Korean war progressed; Lyndon Johnson, 32 points during the Vietnam war; George W. Bush, 43 points during the war in Iraq.

to be fair, George W. Bush was terrible at domestic policy, and often seemed to simply ignore it. You can't do that as president. But clearly, involvement in an unpopular war brings down the "heading in the right direction" index, which eventually hurts the party in power, even when the other party started it and ruined it.