The U.S. Congress is again preparing to tackle one of the thorniest social issues in contemporary America — what to do about the thousands of illegal aliens attempting to cross U.S. borders every year as well as the millions who are already here.

"It is affecting every member of Congress in their district back home, it is a top-tier concern," said Rep. John Shadegg (search), R-Ariz.

Shadegg said the issue is gaining so much attention from the public that border security trumped White House marketing of Social Security reform.

"We were at home aggressively doing town halls on Social Security and people were saying 'Hey, wait a minute, what about illegal immigration?'" Shadegg said.

Click in the box to the right to watch a report by FOX News' Major Garrett.

An estimated 700,000 illegals entered America last year; the national total is nearly 11 million.

California and Texas lead the pack of states, with nearly 4 million illegal aliens combined. Florida follows with 850,000, New York with 650,000 and Arizona has 500,000. Illinois, New Jersey and North Carolina all top 300,000 while another 3.1 million are scattered among the other 42 states.

"The big shift this year is that something has to be done. In the past, immigration has been one of those issues that politicians would just as soon stay away from," said Frank Sharry, executive director of the National Immigration Forum.

That is no longer the case on Capitol Hill, where lawmakers are boosting border patrol funding and drafting bills to penalize businesses that hire illegals.

"If we aggressively go after the employer — the people who are creating the demand side of the equation — I assure you that in vast numbers people who are currently here illegally will return to their country of origin because they won't have a job," said Rep. Tom Tancredo, R-Colo.

Politically, the White House is now playing catch-up. President Bush's plan to legalize millions of alien workers, giving them guest worker status, has fallen flat on Capitol Hill. A comment in March in which the president described the Minutemen, a group of volunteer civilian border monitors, as "vigilantes" only made matters worse.

Days after the president's remark, more than 700 Minutemen (search) helped authorities dramatically reduce the number of illegal crossings on the Arizona-Mexico border. Some Republicans still recoil at the president's use of the term.

"I think on that one he missed the mark," Shadegg said.

Senior Bush advisers are crafting a new immigration proposal — one with more emphasis on border control and less on legalizing illegal workers.

But that hasn't been easy. Nearly 7 million illegals hold down jobs in the United States, half in the construction and service sectors.

"You can say, 'Gee whiz, I wish they wouldn't come' or 'I wish they weren't here,' but the reality of our labor market is we need these workers for the new jobs that are being created in the service sector because we're sending our kids to college not to be busboys or housekeepers," Sharry said.

On top of that, almost no one favors mass deportations of employed illegal aliens

"Rounding them up and shipping them back is not a possibility. Granting them blanket authority and rewarding them for having come illegally is not a possibility," Shadegg said.

Congress will tighten border security, but two other issues remain — how to create verifiable documents that employers can use to separate legal from illegal workers, and how to grant legal status to millions of illegals with jobs, families and U.S. connections without granting blanket amnesty. Many lawmakers say they want aliens to go home before winning legal status in the United States.