CYNICS IN CONGRESS, eager to derail landmark legislation to overhaul the nation’s broken immigration system, have seized on last week’s events in Boston as a pretext to slow momentumon the issue. In the process, they may unwittingly provide a push for the very bill they hope to derail.

With scant regard for the actual immigration status of the bombing suspects, who came to this country legally as minors, Sen. Charles E. Grassley (R-Iowa) nonetheless framed the attacks in Boston in the context of the debate over immigration. With a suspect still at large Friday, he asked, “How do we ensure that people who wish to do us harm are not eligible for benefits under the immigration laws, including this new bill before us?”

His fellow Republican, Sen. Rand Paul of Kentucky, then sent a letter to Senate Majority Leader Harry Reid (D-Nev.), arguing that the Senate “should not proceed [with immigration reform] until we understand the specific failures in our immigration system.”

Just what flaws in the immigration system are the senators talking about? The failure to divine the future and predict that Tamerlan Tsarnaev, who was a teenager when his family immigrated, and his surviving brother, Dzhokhar, who was 9, might become radicalized years after arriving?

In fact, the senators aren’t raising real questions about immigration; they’re more interested in stirring fear: fear that immigration reform may somehow open America’s gateways to even more scary foreigners, and more terrorist attacks, and that undocumented immigrants already here, who would receive legal status under a Senate bill, would be threats in our midst, free to circulate as they please.

One potential casualty of playing politics with immigration reform in this way is the refugee asylum program, which has been at the heart of America’s immigration system for years. (It was as asylum-seekers that the Tsarnaev family received permission to stay here.) Hundreds of thousands of refugees have arrived on these shores over the years as asylum-seekers; minuscule numbers of them have posed any threat to national security.

From what is publicly known, if any governmental failure allowed the suspects to slip through the cracks — and that’s far from certain at this point — it was an intelligence failure, not an immigration failure. The real immigration failure is the perpetuation of a system that forces 11 million undocumented migrants, most of whom have been here for more than a decade, to live and work in the shadows.

By extending legal status to undocumented residents, immigration reform would bring them into the sunlight. In the process of applying for documents, they would be identified, subjected to fingerprinting and background checks and, ultimately, integrated into American society. That could only enhance the nation’s security, and it’s one of many powerful arguments for reform.

Too many opponents of immigration reform still cling to the fantasy of mass deportation. Seeing the Boston bombing suspects as convenient catalysts, they hope to galvanize the nation’s anger. That tactic has worked at times in American history. It mustn’t be allowed to work now.