I don't know how prominent it is in the States, but Canadian politicians at municipal, provincial, and federal levels do this all the time. Personally I hate politicians that pull this bullshit. You're getting into politics to change things on the scale of the province/nation you're residing over. Donating your salary isn't going to make a bit of difference on a national or provincial scale, it's a cheap way to win votes through useless guesteres IMO. It's sort of like "if you vote for me, you'll be supplying money to a good cause!". Votes shouldn't be based on that, they should be based on good governance.