Boing Boing came across this recent video of Franken drawing all 48 states (of the continental U.S., geography nerds) from memory at the Minnesota State Fair, and ever the paranoid types, wondered if Franken is faking it: "it would be easy to create indented trace-lines by using a pen with no cartridge in advance." Doubtful given how long and how often Franken's been doing this trick.
The first time I saw Franken draw his map was on Saturday Night Live when he was analyzing presidential election results (I think 1988?) but I can't find a video of it online. But there is a Youtube clip from 1987 of Franken on Letterman drawing his map in under 2 minutes (he starts at about the 7:30 mark). It doesn't look like his technique has changed much since, aside from now adding in Hawaii and Alaska.
Apparently, he did his map-drawing trick regularly at fundraisers during his Senate campaign. Last July, map blog The Map Room posted a video from 2007 and Daily Kos has some pictures from August of last year. Leave it to the U.S. Senate's greatest hope for (intentional) comedy to only give us his wonkiest, two-decade old joke.