The Green Party
This is an easy one. Green Party members are likely clamoring to get behind the wheel of the all-new 2010 Honda Insight, a beacon of modern, efficient transportation. Their second choice would be the 2010 Toyota Prius, a car they may have chosen first if they didn't already own a previous version.
Because of their general distain for big business - a bias seemly aimed at only American corporations - Green Party members wouldn't be caught dead in domestically-produced hybrids. Too bad. For greenies without sufficient funds for something new, they'll continue driving ancient Volvo 240 wagons, happily spewing more emissions per mile than a Bugatti Veyron, but the Volvo has the right image.
The Libertarian Party
Libertarians should all drive Vipers. Built on Mack Avenue in Detroit proper, this Dodge entrusts pilots with 600 horsepower and no traction or stability control programs. The fate of Viper drivers remains solely in their own hands, after all, with great power comes great responsibility.
Libertarians promulgate governmental laissez faire resulting in policy views that minimize government control over life in general; they're anti income tax, anti gun control, and anti just about everything else big government meddles in. Perhaps if more Libertarians actually drove Vipers, they'd add an anti speed limit plank to the platform. That would get our vote.
The Michigan Militia
If the Michigan Militia were still as popular as it were after 9/11, their more successful members would drive 2006 Hummer H1 Alphas, the final and best genuine Hummer ever produced for the civilian market. Less successful party regulars would drive surplus HUMVEES retired from active duty. The most popular color would be, what else, camo. In lieu of Hummers, any domestic pickup will suffice. Party status is elevated by heavy-duty models with diesel power.