No need to define the term for me.
It is obvious that the term refers to undermining the troops in the field by causing unnecessary political dissent at home.
For example: The Democrats want to cause a "quagmire" in Iraq because they think it benefits them politically to have the war continue on and on indefinitly. The last thing they want is a quick end to the war. That would be the opposite of a "quagmire", and that would signal a Bush victory, and that is unacceptable to the Democrats.
In short: the Democrats want more amerian soldiers in a "quagmire" of death and destruction because that undermines Bush and thus benefits them politically by allowing them to say smirkly the words "I told you so".
See also "self-fulfilling prophacy".