There's a history of Congress saying "no" to troop escalations....

[marmar]

from a Center for American Progress article:

As the examples below demonstrate, past Congresses have chosen among several different policy levers to guide U.S. national security policy as it relates to the deployment of American troops. Broadly speaking, the Congress can:

Condition, limit, or shape the timing and nature of troop deployments and the missions they are authorized to undertake;
Cap the size of military deployments; and
Prohibit funding for existing or prospective deployments.
Since 1970, there have been several instances in which these powers were exercised and passed into law by Congress. Several of these are detailed below. Each of these provisions reflects the basic fact that the Founding Fathers deliberately created a system of government containing branches that were both interdependent and competitive. Each has a specific role to play and each needs to respect the role of the other branches. While the president is commander-in-chief, Congress retains the power (with the consent of the president) to establish the laws by which the United States conducts foreign policy and more importantly, to decide whether the activities in which the president is engaged are deserving of the resources from the American people he requests to conduct those policies.

Additionally, there have been hundreds of amendments—which did not ultimately become law—where members of Congress sought to shape overseas deployments. These amendments reflect modern congressional understanding of Congress’s power and authority. In particular, there were a series of attempts by Republicans and Democrats throughout the 1990s to influence deployments in the Balkans. Though largely unsuccessful on policy grounds, the provisions—an illustrative list of which appear at the back of this document—were attempted by prominent Republicans and Democrats, many of whom remain involved in today’s debate on Congress’s role in national security policy. What was true then remains true now: Congress has an obligation to remain engaged on shaping national security policy.

Examples of Funding and Authorization Limitations Enacted into Law

January 1991. P.L. 102-1 – A joint resolution authorizing the use of force against Iraq. Congress granted the president the authority to use force in Iraq but conditioned it on him first certifying that means other than war would not result in Iraqi compliance with UN Security Council resolutions.

October 1994. P.L. 103-423 – A joint resolution regarding U.S. Policy Toward Haiti. Congress supported a “prompt and orderly withdrawal of all United States Armed Forces from Haiti as soon as possible.”

September 2001. P.L. 107-40 – A joint resolution authorizing the use of force in Afghanistan. The president initially sought authorization to use force to “deter and pre-empt any future acts of terrorism or aggression against the United States.” The final resolution authorized “all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided” the 9/11 attacks.

October 2002. P.L. 107-243 – A joint resolution authorizing the use of force in Iraq. Like the Afghanistan resolution a year earlier, the Iraq resolution reflected some changes sought by Congress. For example, the president initially sought authorization to use force “to restore peace and security in the region.” Congress succeeded in striking that provision, and made the exercise of the authority granted in the resolution conditional on the president certifying that Iraq would not harm the war on terrorism, but it failed in attempts to insert other limitations on the president.

Troop Caps Enacted Into Law

December 1974. P.L. 93-559 – Foreign Assistance Act of 1974. The Congress established a personnel ceiling of 4000 Americans in Vietnam within six months of enactment and 3000 Americans within one year.

June 1983. P.L. 98-43 – The Lebanon Emergency Assistance Act of 1983. The Congress required the president to return to seek statutory authorization if he sought to expand the size of the U.S. contingent of the Multinational Force in Lebanon.

June 1984. P.L. 98-525 – The Defense Authorization Act. The Congress capped the end strength level of United States forces assigned to permanent duty in European NATO countries at 324,400.

July 2000. P.L. 106-246 – Military Construction Appropriations and For Other Purposes – Personnel Ceiling in Colombia: “no funds appropriated or otherwise made available by this or any other Act (including funds described in subsection (c)) may be available for— (A) the assignment of any United States military personnel for temporary or permanent duty in Colombia in connection with support of Plan Colombia if that assignment would cause the number of United States military personnel so assigned in Colombia to exceed 500; or (B) the employment of any United States individual civilian retained as a contractor in Colombia if that employment would cause the total number of United States individual civilian contractors employed in Colombia in support of Plan Colombia who are funded by Federal funds to exceed 300.”


Funding Restrictions Enacted into Law


December 1970. P.L. 91-652 – Supplemental Foreign Assistance Law. The Church-Cooper amendment prohibited the use of any funds for the introduction of U.S. troops to Cambodia or provide military advisors to Cambodian forces.........(more)

The complete piece is at: http://www.americanprogress.org/issues/2007/01/military_deployments.html