"We cannot simply speak out against an escalation of troops in Iraq, we must act to prevent it...There can be no doubt that the Constitution gives Congress the authority to decide whether to fund military action, and Congress can demand a justification from the president for such action before it appropriates the funds to carry it out."[1]
Simple: We cannot just say "No" about sending more troops to Iraq. We must do something to stop it. The Constitution allows Congress to decide whether to fund for the military. We [the Congress] want a good reason from the President why we should fund the Iraq War.
About the quote: While talking about the Cape Wind Project, as quoted in Cape Wind: Money, Celebrity, Class, Politics, and the Battle for Our Energy Future on Nantucket Sound (2007) by Wendy Williams and Robert Whitcomb.