In a letter to the Senate majority leader, Republican Rand Paul says national security questions surrounding the Boston bombings need to be addressed before Congress deals with comprehensive immigration reform. The terror attacks at the Boston Marathon last week were allegedly perpetrated by the Tsarnaev brothers, who are ethnic Chechens and immigrated to the U.S. a decade ago.For some that is reason to be cautious on who the country is allowing in as lawmakers deliberate overhauling the immigration system. Others argue conservatives are only seizing on their ethnicity of the accused bombers to stoke nativist fears and derail reforms.Paul is urging Senate Democratic Leader Harry Reid to incorporate various national security concerns first and is openly asking if systemic failures allowed the two men to enter the U.S. without further background checks.From Paul's office: The facts emerging in the Boston Marathon bombing have exposed a weakness in our current system. If we don't use this debate as an opportunity to fix flaws in our current system, flaws made even more evident last week, then we will not be doing our jobs. 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 is calling for hearings in the Senate Homeland Security and Government Affairs Committee to study the national security aspects of this situation.But some conservatives—such as Paul's chief GOP rival and immigration reform leader Sen. Marco Rubio— are beginning to push back. On Twitter, Rubio said the Boston bombings are not an excuse for inaction but that flaws need to be fixed.Anonymous GOP aides have also expressed that support for immigration reform remains the party's top priority.UPDATE:Asked about Paul's letter to Reid, Congressman John Yarmuth, D-Ky., who is working on immigration reform as part of the House 'Gang of 8' told WFPL the senator's implication is off the mark."National security and public safety have always been integral parts of comprehensive immigration reform. To imply that they wouldn’t continue to be top priorities is absurd," he says.Other critics have pointed out that a number of terror attacks have been committed by native-born Americans such as Timothy McVeigh, who was responsible for the Oklahoma City bombings in 1995.Historically speaking, linking immigration to terrorism has been a century old debate.From The Economist: The first push to restrict immigration in the 20th century got started after anarchist Leon Czolgosz assassinated President William McKinley; he wasn't even an immigrant himself, his parents were, but it was enough to prompt Teddy Roosevelt to ask congress to bar "the coming to this country of anarchists or persons professing principles hostile to all government". The resulting Anarchist Exclusion Act of 1903, and the Immigration Act of 1918 which expanded its authority, didn't end up actually kicking out more than a few dozen people. And the 1924 Immigration Act, which really did lead to a drastic cutback in immigration, was based on quotas by race and country of origin rather than ideology. But the political discourse supporting immigration restrictions has always leaned heavily on supposed threats of violence, both criminal and ideological.