Dear Senator Lieberman,
You aren't my Senator, but there's no campaign finance law restricting cross-state donations. It will be another three years before you're up for re-election. I will be supporting your opponent, even if that means supporting the Republican challenger. The change won't be that much even in that case. And I mean to do this even if it gives the Republicans 60 votes in the Senate.
I don't mind principled stands on issues. As an elected official myself I understand them and know why they are sometimes necessary. However, you've shown yourself to be a small tyrant. One willing to offer a compromise only to yell, "psych!" and withdraw his support even when he gets what he was offering.
Thank you for your time. Don't let the door slam your ass on the way out.