Former Pennsylvania senator Rick Santorum’s heated outburst at a New York Times reporter on the campaign trail in Wisconsin on Sunday is getting lots of national attention as the political class asks why Santorum lost his cool so badly.

U.S. Republican Presidential candidate Rick Santorum speaks outside the Supreme Court, during the first day of legal arguments over the Affordable Care Act, in Washington March 26, 2012. REUTERS/Jason Reed

Take this clip of a 2006 debate between Santorum and then state Treasurer Bobby Casey Jr. (D). Fast forward to the 2:30 mark. (Special thanks to NBC’s Brooke Brower for pointing us to it.)

First of all, who decided to put the candidates’ podiums one inch from one another? (Can you say “awkward”?) Second, it’s clear that Santorum loses his cool — or comes darn close to doing so — several times in that 90-second (or so) clip.

And Santorum seems to sense it too. In his closing remarks at that debate, Santorum said: “I am a passionate guy. I’m tough. I‘m a figher. I’m an Italian kid from a steel town.”

Passion and toughness are good things in politics. Anger and temper are bad things. And there is a very fine line between the two. (In the words of David St. Hubbins: “It’s such a fine line between stupid and clever.”)

Santorum, who has stayed on the right side of that line for the majority of the campaign, has found himself drifting in the past few days. The image of an angry Santorum isn’t a winning one. If Santorum needs a reminder of that fact, all he needs to do is go back and pore over the 2006 election results.