With a comprehensive U.S. immigration reform bill garnering more than 80 votes twice on the Senate floor Tuesday, there is no doubt about the strong bipartisan consensus to debate the issue. That said, the procedural votes don’t indicate such overwhelming support to see the legislation passed by the end of 2013.

What's more, New York Sen. Chuck Schumer’s quest to attract 70 votes for the measure seems to be making some of his top Democratic colleagues a bit uneasy. They would much rather him play it safe -- that is, go for merely a 60-vote threshold, the number needed to avoid a potential filibuster. A senior Democratic aide said Deputy Majority Leader and Whip Dick Durbin, D-Ill., and Majority Leader Harry Reid, D-Nev., want the “strongest bill possible with as many votes as possible.”

However, on Wednesday Reid said he would like to keep the core principles intact.

“[This bill] does not and should not make the path to citizenship contingent on attaining border security goals that are difficult to measure,” Reid said. “That could leave millions of people who aspire to become citizens in limbo indefinitely.”

But some experts think a more right-leaning immigration reform bill will be leaving the upper chamber. This could mean a bill that puts greater importance on border security and enforcement than legalizing the 11 million undocumented immigrants current in the country. That’s the prediction of Alex Nowrasteh, an immigration policy analyst for the Cato Institute.

Despite major gains in border security over the years and an additional $6 billion appropriation for it in the current bill, some Republicans still insist more needs to be done to curb future illegal entry, particularly on the southern border.

“Politically [border security] is a very strong argument, but factually the number of border crossers is at about a 40-year low as far as we can tell with current statistics,” Nowrasteh said in an interview earlier this week. “So the success that additional [resources] will cause on the border in decreasing illegal immigration is very minimal because immigrants are drawn to the United States because of economic opportunity, and what has decreased immigrant crossings is not increased enforcement but decreased opportunities when they come here.”

According to a 2011 study by the Center for American Progress, the flow of illegal immigrants at the southern border has dramatically decreased. In areas such as the San Diego sector, where there were more than 565,000 apprehensions in 1992, there were only 151,000 in 2010 because of fencing and more boots on the ground.

That’s not to say some sectors along the southern border aren’t still very challenging. The same study showed that apprehensions in the Tucson sector were more than 616,000 in 2000. Though that figure has dropped significantly (by more than 200,000 between 2000 and 2010), that portion remains a challenge. When looking at these figures researchers say the “numbers tell us that we no longer have a border across which thousands of people traverse illegally every day without our knowledge. Instead, we have a border where the vast majority of attempted entries are identified and a far larger percentage of entrants are apprehended than ever before.”

Still, some lawmakers, like Sen. John Cornyn, R-Texas, want to make a path to citizenship contingent on border security. His proposed amendment requires 100 percent monitoring of all parts of the Mexican border and a 90 percent apprehension rate. Some of his Senate colleagues have called this a “poison pill.”

Whether such an amendment stands a chance is still anyone’s best guess.

“We’re willing to entertain amendments [that] don’t damage the core principles of the bill but improve the bill just as we did in committee,” Schumer, D-N.Y., said Sunday on MSNBC’s “Meet the Press.”

And advocates are hoping the present legislation, which they admit is imperfect but reasonable, won’t be eroded just to pack a punch in the House. They would much rather advance a reformist bill with 60 votes than a bill with its core principles shattered.

“I know within the advocacy community we’d like it to be a strong vote,” said Philip Wolgin, senior policy analyst for immigration at the Center for American Progress. “The stronger the vote, the better going into the House, but we are definitely more interested in getting a good bill at, say, 65 or 60 votes than giving up the core of the deal to get 70 votes.”