Everyone knows President Bush left office with record disapproval rating of 67{09f965da52dc6ab4c1643a77bd40d1f729d807040cd8db540234bb981a782222} (from January 2009 NBC/WSJ survey). And it’s been part and parcel of the Democratic strategy to continue running against the former president. The Democrats who run campaigns aren’t idiots; they did it because it worked.

So, how long will the Bush Hangover last?

Combining the inflation rate plus the unemployment rate form a handy stat known as the “Misery Index.” Handy for pols because it is directly connected to Americans’ desire for change.

The Index was created by LBJ economist Arthur Okun and went public in 1976, when it became a staple in Jimmy Carter’s campaign against Gerald Ford. (See attached chart: Carter was killed with his own sword four years later). When we connect the dots between the Misery Index and election results, it tells us that Americans have little in the way of short-term memories and vote largely in the present.

How does the W’s 10.16 Misery Index measured October just prior to 2008’s Obama landslide stack up?

And there lies the first of several morals to this story: Bush’s Index was poor, but clearly not the worst. Second, it is VERY difficult for a party to maintain its hold on power when the Misery Index gets into the “8s” and extremely difficult when it gets into double-digits.

Presidents can defy gravity, but their party can’t. In November of ‘56, Ike coasted to reelection on the back of a 6.13 Index. But, by the fall of ‘58, the Index had risen to 9.22 and the Democrats won 48 more House seats and 13 more in the Senate. Nixon trounced McGovern in ‘72 (9.02 in October) but lost 48 House and five Senate seats in ‘74 (18.06).  Reagan won 49 out of 50 states against Mondale in ‘84 (11.66) but for the mid-terms, the Index was 8.75 and the GOP lost eight Senate seats.

Which brings us to the moral of the story. Americans have a short term memory when it comes to change and are likely to change again if things don’t improve.

When President Reagan beat President Carter in ‘80; the Index was a whopping 20.27. But in 1982, blaming Carter didn’t work, the Index stayed high and Republicans lost 26 seats in the House as the Democrats rode a 15.54 Index into the November elections. In ‘92, President Clinton beat President Bush (‘41) with the “It’s the Economy, Stupid” campaign, aided by an Index of 10.5 going into November. What happened next? The Index stayed generally high (8.41 in October ‘94) and Republicans took the House and Senate.

So, where is President Obama today? The Index was 7.63 at the start of the year and 12.4 as of the beginning of the month, or a huge 625 basis point increase and rising. If President Obama and the Democrats maintain a double-digit Misery Index into the 2010 elections, “Crying Bush” will be of little help. However, if it drops into the mid-single digits, expect little in the way of change. Hint: with unemployment, half of the Index math, hitting high single digits by itself, this low of an Index could be a tall order for Democrats to achieve by 2010.