I think they'll shelve that proposal as long as the British sailors are being held. If not then they've really gone off the deep end (I mean even more so than we'd thought at any rate).
According to them, everything is Bush's fault. Every bad thing that happens in the world is an opportunity to criticize the administration and attempt to grab more power.
They have chosen sides in the war in the middle east. If the US and her allies win, the Democrats lose.
The absolute last thing the Dems want is for the US to invade Iran, because we will demolish them militarily. We will also throw their terrorist network into disarray. We will spread their forces and resources thinner.
Their ability to fund and organize insurgencies in Iraq and Afganistan will weaken, at least for a time.
They are afraid that the conflict will expand, because any successes will hurt them in the 2008 elections, and no one trusts the Dems to win a war, and if the war starts looking winnable, the Dems will lose their support among swing voters quickly.