With just days before the next set of Democratic primaries, the idea of a summer "gas tax holiday" is working its way to the economic forefront, and become a rare flashpoint of policy disagreement between Sens. Hillary Clinton and Barack Obama.

Clinton has suggested suspending the 18.4 cent-per-gallon tax on gasoline, while Obama has attacked the idea as political pandering. But the merits of the idea haven't received much evaluation on the stump.

To fund her plan,...