Sen. Rand Paul (R-Ky.) on Monday threw some cold water on the just-begun process of debating new immigration legislation, saying any such push should be delayed until after the country can address why the two suspected Boston bombers were allowed to immigrate to the United States.

"We should not proceed until we understand the specific failures of our immigration system," Paul said in a letter to Senate Majority Leader Harry Reid (D-Nev.). "Why did the current system allow two individuals to immigrate to the United States from the Chechen Republic in Russia, an area known as a hotbed of Islamic extremism, who then committed acts of terrorism?"