There are pundits out there who are saying that the Democrats want the US to fail in Iraq so that they (the Democrats) can win in the November elections. Let's put that one to rest right now.
Democrats win on domestic issues not the results of foreign wars. Hence, if the concerns Democrats focus on are okay, that is, if the economy is doing well, if unemployment is not really out-of-line, the Republicans win.
Conversely, Republicans win during times of war or unrest. If anyone needs the "war on terrorism" to continue it is the Republicans. Remember how the country rallied round the President after September 11th? Well, if any one needs the fear that comes with war, whether in Iraq or elsewhere, it's the Republicans because they know as soon as the war ends, so do they.