Looking at 13 historical episodes ranging from the bombing of Pearl Harbor to the Sept. 11 terrorist attacks, the folks at POS found that the average presidential bump was 13 percentage points and it took an average of 22 weeks (or five months) for the president’s numbers to return to their pre-incident levels.

The longest sustained bump? 105 weeks for President George W. Bush in the wake of the Sept. 11 attacks. The shortest? Four weeks for President Ronald Reagan after his first summit with Russian President Mikhael Gorbachev.