Kentucky Sen. Rand Paul is vowing to "everything possible" to terminate the terrorism-era Patriot Act, but the Republican presidential hopeful concedes that it may not be enough.

Paul on Monday lashed out at the National Security Agency's bulk collection of American citizen phone records in the name of preventing acts of terrorism. The Kentucky senator made the comments during an event outside Philadelphia's Independence Hall.

Paul acknowledged there aren't enough votes in Congress to block legislation renewing the Patriot Act, but he promised to try to filibuster the measure this week. The surveillance program will expire on June 1 unless Congress acts.

The federal government's surveillance programs could play prominently in the GOP presidential primary contest. Some of Paul's Republican competitors support the programs.