Sen. Rand Paul’s latest entry into the immigration debate has drawn a measured response from the top Senate Democrat.

Senate Majority Leader Harry Reid responded Tuesday to Kentucky Republican’s call to include national security lessons learned from last week’s Boston bombings in immigration legislation. Reid highlighted security provisions already in the “gang of eight” immigration proposal.

“The bipartisan immigration reform proposal introduced last week would enable us to identify and perform criminal background and national security checks on immigrants who are here unlawfully,” the Nevada Democrat said in a Tuesday letter.

Paul sent Reid a letter on Monday calling for hearings and further review of immigration background check procedures before moving forward with immigration legislation in the aftermath of last week’s bombing at the Boston Marathon and subsequent police standoff in the Boston area. Paul’s missive was spurred by the fact that the two brothers suspected of perpetrating the terrorist attack are legal immigrants. Tamerlan and Dzhokhar Tsarnaev arrived in the U.S. as children with their ethnic Chechen parents, who sought asylum.

“We should not proceed until we understand the specific failures of our immigration system. 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? Were there any safeguards? Could this have been prevented? Does the immigration reform before us address this?” Paul wrote Monday.

Perhaps in part because Paul has been generally supportive of an immigration overhaul, Reid offered only a mild rebuke, highlighting ongoing work by the Senate Judiciary Committee and other panels, including Homeland Security and Governmental Affairs, on border security. Reid also renewed his pledge to bring the bill to the floor with a robust amendment process.

“There will be ample opportunity to amend this bill, both in committee and on the floor, as it moves through regular order,” Reid wrote. “I look forward to working with you throughout this process on ways we can improve this bill and enact commonsense immigration reform that will enhance our national security, improve our nation’s economy, keep families together, and fix our broken system once and for all.”

Judiciary ranking member Charles E. Grassley, R-Iowa, told reporters Tuesday that, as is customary under committee rules, the Judiciary panel would hold over the legislation for a week before calling it up for consideration at one of the panel’s usual Thursday morning markups. Grassley said at this point he has read about 50 of the more than 800 pages in the bill and would reserve further judgment until he has time to review it.

The Judiciary Committee also on Tuesday completed three successive days of hearings on the bill, and a major topic of discussion included some senators attempts to link the immigration debate and the Boston bombings. Gang of eight members, however, have been aggressive in combating the notion that the bill should move more slowly because of the tragedy in Boston.