The Office of Management and Budget alerted federal agencies to prepare for a limited shutdown at midnight Thursday as Sen. Rand Paul, R-Ky., took to the Senate floor to block passage of a sweeping budget deal that would increase spending by more than $300 billion over two years. The government is operating on its fourth short-term spending bill - which expires at midnight - because Congress has been unable to agree on a full-year budget. The budget deal is attached to a short-term spending measure that will keep the government open until March 23, giving lawmakers time to write a full-year bill. If the Senate passes it, the legislation still needs to go to the House for final approval.