Normally, when a member of the minority offers an amendment to a spending bill, it's routine for his fellow minority party members to support the amendment, while the members of the majority party vote it down.

What's fun is to examine the rebels -- the members who cross party lines to cast votes against their fellow party members -- to see if you can figure out why.

This afternoon, on the Transportation-HUD appropriations bill, the Senate voted on an amendment by conservative South Carolina Republican Jim DeMint "to limit the use of funds for the John Murtha Johnstown-Cambria Airport."

That, you may recall, is the airport where there are more federally funded employees and buildings than there are daily passengers -- which isn't difficult, given that it has only three regularly scheduled flights per day.

In other words, DeMint forced the Senate to vote whether the Murtha Airport would receive more government funds (at least from the Transportation-HUD appropriation bill) than the $800,000 in stimulus package funds it received earlier this year.

Not surprisingly, the amendment was defeated, 43-53.

Also not surprisingly, almost every Republican voted for the amendment, and almost every Democrat voted against it.

So the fun part is figuring out the motivation behind the Republicans who voted against it and the Democrats who voted for it.