Key Patriot Act anti-terror provisions, including bulk collection of Americans' phone records, expire at midnight unless senators come up with an 11th hour deal in an extraordinary Sunday afternoon session.

Chances for that look all but nonexistent. Republican Sen. Rand Paul of Kentucky, who is running for president, vowed Saturday to force the bulk phone collection program to expire. And the Senate's complex rules allow him to do just that — at least temporarily.

A House-passed bill backed by the White House that remakes the National Security Agency phone collection program is just three votes short in the Senate. But even if it picks up the needed support despite opposition from Senate Majority Leader Mitch McConnell, moving to a final vote requires the assent of all senators.