Political debate is rife with this one, and I've been the subject and a focus of this type of attack countless times at LCL.com. I thought it would be helpful to make it the focus of this weeks fallacy. Again, this article is not meant to be the exhaustive work on the subject.
Defined
Poisoning of the Well is very simple. The petitioner will offer some unfavorable information that they think will discredit their opposition. This information can be either true or false. The attack is made to spread suspicion without actually having to address the merits of the oppositions arguments or beliefs.
Examples:
01. Hamas had nice things to say about Barack Obama. Therefore Obama is a weak on defense and will destroy the county.
02. George Bush said "If this were a dictatorship, it would be a heck of a lot easier......just so long as I'm the dictator." Therefore, Bush will turn the US into a dictatorship and destroy the county.
In example one, whether or not some organization had nice things to say about Obama does not change what policies (Palestinian Anti-Terrorism Act of 2006) and what statements (Obama's speech to AIPAC June 6, 2008) he has made in the past. Hamas later retracted, and McCain's campaign applied Hamas quote out of context in order to spread fear and suspicion.
For example two, despite the fact that Bush stated this does not mean he wants to transform the U.S. into his own private kingdom and that every policy decision he makes is a step toward this goal. Whether the policy is domestic like No Child Left Behind (Vote), or foreign, like the Iraq War (Joint Resolution on Iraq) these would not have become reality with or without tacit compliance from Congressional Republicans and Democrats alike. Bush still has to rely on the legislative process in many cases. Also, this quote is often used out of context.
As a side note, I really wish I had a nickel every time when either some Democrat or Republican used one of these.
In Conclusion
Both of these examples are non-sequiturs as the conclusions we are being led into are not supported by the evidence. In fact, the evidence (if we bother to check) rebukes this type of indirect ad hominem attack. Honest debate should be about the merits of a policy or a belief, and not made as an attack through fear and suspicion.