Even with a bipartisan budget deal in hand, it would only take one lawmaker to block the accord and shutter the government.
With little more than 2 hours before the midnight deadline, House and Senate leaders will need to pass some type of funding measure by unanimous consent to avert a shutdown.
If one legislator balks, the government will shutter.
Under the rules of the Senate, a bill cannot be moved quickly unless it clears by unanimous consent. If there is an objection, a cloture motion must be filed and approved -- a process that takes days.
Time is also running short for action in the House. Like the Senate, a temporary measure could be approved by the lower chamber by unanimous consent or voice vote, but a small group of lawmakers can demand a roll call vote.
If a small group objects, House leaders would have to scramble to convene the Rules Committee to schedule a quick vote, but they would have to race to beat the midnight deadline.
Updated at 11:20 p.m.