“After something like that happens, they should stop all visas, for crying out loud,” said Ms. Kontis, 58, who owns New Wayne Pizza with her husband, Alex. “It’s insane. It just angers me.”
 
Ms. Kontis was born in Greece and immigrated to the United States as a child, but when two men of Chechen heritage were identified as the suspects in the fatal Boston Marathon bombings, her usually broad views about immigration became colored by concerns for national security.
 
“That is who’s coming in,” she said. “We don’t know what kind of people they are. The bottom line is we have to stop being goody-goody Americans.”
 
As a national debate over major immigration reform begins in Congress, some opponents are pointing to the Boston bombings as cause for concern about expanding visa programs and offering millions of illegal immigrants a path to citizenship.
 
On Friday, Senator Charles E. Grassley, a senior Iowa Republican on the committee debating the plan, which is proposed by a bipartisan group of eight senators, said the terrorist bombings should figure into the debate. Some conservative commentators and Congressional Republicans want to shift the focus away from economic and humanitarian concerns to border security and the potential threat from terrorists entering the country.
 
How successful their efforts turn out to be, and whether Boston slows momentum for change, could depend on how many citizens express views like Ms. Kontis’s.
 
But judging by a sampling of voters in one politically divided region, the western suburbs of Philadelphia, the Boston bombings may be an imperfect test case for opponents of reform.
 
In interviews Friday night, as the denouement of the manhunt played out in the hours when people gathered in taverns or strolled the streets on a pleasant evening, many mentioned that the two brothers linked to the attacks — Dzhokhar A. Tsarnaev, 19, who was captured Friday, and Tamerlan Tsarnaev, 26, who was killed earlier — had arrived in the country a decade earlier, with a father who claimed asylum because of the conflict in their homeland. They could hardly have been identified by more vigilant border control, people said.
 
“You can’t stop people who came into the U.S. who 10 years later do bad things,” said Andrew Factor, 26, an investment adviser who stopped outside his office on the main street here. “We’re supposed to screen for terrorists when kids are 9 and 16?”
 
Nonetheless, the details of the Tsarnaev family’s odyssey may become lost in a larger debate over immigration policy, an issue that evokes visceral reactions. Two Republican senators favoring reform, Lindsey Graham of South Carolina and John McCain of Arizona, warned Friday of bringing Boston into the debate and insisted an overhaul would tighten security “by helping us identify exactly who has entered our country and who has left.”
 
But that message was not always embraced. “I’m a little more of an extremist now after what happened in Boston,” said Greg Ricker, 41, a stockbroker, as he stepped outside the Flying Pig Saloon in Malvern for a cigarette. “I think we should just stop letting people in.”
 
Like nearby Wayne, Malvern is part of a suburban belt that has grown more Democratic in recent elections. Attitudes toward immigration reform seem to be changing, in part along generational lines. Frank Cunningham, a 27-year-old accountant, said that he, unlike his father, favors a path to citizenship for the estimated 11 million illegal immigrants in the country.
 
“The way I was raised, my dad says, ‘If you come into the country illegally, you don’t deserve to be here,’ ” Mr. Cunningham said. “But I’m wondering who is going to do those jobs?”
 
Gary Burnett, 35, said he favored a path to citizenship and expanded permanent-resident visas for those waiting outside the country, because the nation is already part of a global economy.
 
As a software engineer, he said, “I compete with the entire world already. I have to be able to do the work of at least three people in Asia to compete.”
 
He thought the potential that some immigrants might turn out to be terrorists was a red herring.
 
Melvin Cook, 57, who was buying a pizza, went further. He accused politicians of exploiting the Boston bombing. “They’re trying to put fear into us of immigrants,” he said. Mr. Cook, a truck driver, said of illegal immigrants, “The jobs they’re getting, nobody wants.”