A top Republican senator used the terror bombings in Boston to raise new questions on Friday about a bipartisan comprehensive immigration reform bill, legislation that now faces growing questions from conservative critics.
Democrats shouldn't rush the legislative process "given the events of this week," Iowa's Chuck Grassley said at the opening of a Senate Judiciary Committee hearing on the nearly 900-page bill.
"It's important for us to understand the gaps and loopholes in our immigration system," Grassley said. "How can individuals evade authorities and plan such attacks on our soil? How can we beef up security checks on people who wish to enter the U.S.?"
"This hearing is an opportunity to refocus on ... the importance of remaining vigilant and secure in our homeland," he added.
One of the bill's authors, New York Democratic Sen. Chuck Schumer, responded by urging fellow senators to "allow the actual facts to come out" before "jumping to conclusions about Boston."
Two other leading Senate Republicans asserted in a written statement released after the hearing that the Boston bombings actually highlighted the necessity for immigration reform.
"Immigration reform will strengthen our nation's security by helping us identify exactly who has entered our country and who has left -- a basic function of government that our broken immigration system is incapable of accomplishing today," said South Carolina's Lindsey Graham and Arizona's John McCain.
"We have 11 million people living in the shadows, which leaves this nation vulnerable to a myriad of threats," they added. "By modernizing our system of legal immigration, identifying and conducting background checks on people here illegally, and finally securing our border, we will make America more secure."
Overall, the issues of border security and economic concerns dominated the first committee hearing on the long-awaited plan, which was unveiled against the backdrop of the deadly Boston Marathon bombings and subsequent manhunt.
Homeland Security Secretary Janet Napolitano was scheduled to testify, but canceled her appearance on Friday morning as the Boston-area manhunt intensified.
"There is a great deal going on in Massachusetts," said Sen. Patrick Leahy, D-Vermont, the panel's chairman. "I hope everybody will understand why the Secretary Napolitano will not be here."
Leahy promised she would testify on the bill at a later date.
Tighter security has long been a key immigration reform demand for many conservatives, who argue that current border controls remain insufficient.
The two prime suspects in Monday's bombings came to the United States in 2002 and 2006, according to a federal official.
Both suspects were in the country legally. One of them became a U.S. citizen last year, an official told CNN.
The bill assembled by the Senate's "Gang of Eight" -- comprised of four Democrats and four Republicans -- would, among other things, commit $3 billion to enhanced border security.
Money would be used to fortify border fences, boost patrols, and acquire surveillance technology from the Department of Defense -- including drones and drone pilots.
The legislation would require constant surveillance of high-risk border areas and require that border officers turn back at least 90% of those who attempt illegal crossings each year.
Vulnerable sections of the border would have to be deemed secure before most of America's roughly 11 million undocumented residents could begin the journey to citizenship.
Some conservatives are skeptical the Obama administration will ever secure the border to their satisfaction. Many reform advocates believe conservatives want to use the border security issue to deny citizenship to undocumented residents.
It's not right to put undocumented residents at the "mercy" of a border security requirement, Leahy argued. And "spending billions more" on border controls, like fences, are not the "best use of taxpayer dollars."
But the bill is a "product of compromise" and "difficult concessions" on all sides, he added.
Testimony from the hearing's two remaining witnesses focused on the economic impact of immigration reform, and whether it would damage job and wage prospects for citizens on the lower rungs of the economic ladder.
"We have an abundant supply of low skilled labor waiting for jobs," argued Peter Kirsanow, a member of the U.S. Commission on Civil Rights. Sweeping legalization of undocumented workers will result in the "leapfrogging (of) those individuals."
And "we're living in a fantasy land" if we think "by a stroke of a pen" the economic prospects of undocumented residents will be significantly improved, he added.