Immigration bill debate sidetracked by Boston terror issues By Richard Cowan and Caren Bohan WASHINGTON (Reuters) - Congressional advocates of comprehensive U.S. immigration legislation were diverted into a sometimes testy debate on Monday over whether the measure should be delayed because of questions arising from the Boston Marathon bombing allegedly carried out by two immigrant brothers. The idea of holding up the legislation gained some ground with the support of Republican U.S. Senator Rand Paul of Kentucky but it was rejected by the highest-ranking Republican in Washington, U.S. House of Representatives Speaker John Boehner of Ohio. Florida Senator Marco Rubio, a Republican sponsor whose continued support is crucial to the bill's survival, took a middle-ground position, saying in a statement that he disagreed with "those who say that the terrorist attack in Boston has no bearing on the immigration debate" but he added that immigration reform could and should address any "flaws" exposed by the attack in Boston. Rubio's remarks came as some conservative commentators and lawmakers continued to seize on the Boston bombings as evidence that an immigration bill should move more slowly in Congress. Dzhokhar Tsarnaev, 19, who was captured Friday night and charged on Monday in the deadly marathon bombing, was a naturalized U.S. citizen. His brother, Tamerlan, 26, who died after a shootout with police early Friday, also was in the country legally and had applied for U.S. citizenship. The brothers had immigrated to the United States a decade ago with their family, which is from Chechnya. The Boston bombings hung over a congressional hearing on Monday as the Senate Judiciary Committee debated a bipartisan immigration bill. Senators on the committee jousted with each other and with witnesses over how last week's attacks should influence the immigration debate. Frank Sharry, head of the immigration advocacy group America's Voice, said the events in Boston could result in "a few more amendments on national security concerns" being debated as the legislation makes its way through Congress. He added that chances of enacting a bill this year remained strong. John Pitney, professor of politics at Claremont McKenna College in Claremont, California, said the fate of the legislation could be tied to whether there are revelations that the Boston attackers were aided by anyone in the United States illegally. "If they were working with others and if some of those others were here illegally, that's the proverbial game changer," Pitney said in a telephone interview. Timing is considered critical to passage of an immigration reform bill in part because of the approach of the 2014 mid-term elections. Members of Congress traditionally shy away from controversial votes on anything in election season. Supporters of the bill, introduced just last week, also are mindful of the fact that immigration legislation backed by President George W. Bush disappeared from the political radar after the attacks on New York and Washington of September 11, 2001. Boehner embraced arguments by supporters that the bill would enhance national security. Asked by Fox News whether last week's Boston tragedy might sideline the legislation because two immigrants are suspected of planting the bombs that killed three and injured 176, Boehner responded: "It may for a couple of days until we understand 'What did our immigration system know and what didn't they know?' Primarily, I'm in the camp of: if we fix our immigration system it may actually help us understand who all's here, why they're here and what legal status they have. Paul has written to Senate Majority Leader Harry Reid suggesting that the Boston bombing should give Congress reason to pause on immigration legislation. "We should not proceed until we understand the specific failures of our immigration system," Paul wrote. 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? Boehner's defense of some sort of immigration bill came as Senate Judiciary Committee Chairman Patrick Leahy also defended bipartisan Senate legislation against attacks in the wake of the Boston bombings. "The bill before us would serve to strengthen our national security by allowing us to focus our border security and enforcement efforts against those who would do us harm," Leahy said, instead of siphoning law enforcement efforts against illegal immigrants who are otherwise law-abiding residents. The Vermont Democrat added, "Let no one be so cruel as to try to use the heinous acts of two young men last week to derail the dreams and futures of millions of hard-working people." Democratic leaders hope to have an immigration bill on the Senate floor for debate in June. In the past, Boehner has voiced support for trying to pass an immigration bill through the House. But he has not gotten into the specifics of what sort of bill should be presented to his chamber, where a significant number of Republicans oppose a pathway to citizenship for illegal residents. Much of the upcoming debate of immigration legislation in Congress will focus on whether 11 million illegal residents should be put on a 13-year pathway to citizenship, as the Senate legislation provides. Under that provision, those who came into the United States illegally or overstayed their visas would have to register with the government if they want to become legal residents as a first step toward citizenship. That would in effect end their lives "in the shadows," as many immigration reform groups call it, as the undocumented currently try to evade deportation. Even though the Senate legislation has bipartisan support, there is some significant opposition to the current bill in the Judiciary Committee, including Senator Charles Grassley of Iowa, the senior Republican on the panel. Grassley's temper flared when Democratic Senator Charles Schumer of New York, one of four Democrats and four Republicans who drew up the legislation, noted that some were using the Boston bombings as reason for delaying legislation. I never said that. I never said that," Grassley shouted at Schumer. Senator John Cornyn of Texas, the No. 2 Republican in the Senate, noted during the congressional hearing that there were several "positive improvements to our immigration system" in the bipartisan bill. But he signaled that the measure faces a tough fight when he criticized border security provisions of the measure and said that "major changes" were needed. Editing by Fred Barbash and Bill Trott