Biden wants immigration reform by end of summer

(CNN) -- Vice President Joe Biden laid out a timetable for his hopes on immigration reform, saying he wants to see Congress pass a bill in the coming months.

"As my grandpop would say, with the grace of god and the good will of the neighbors, Congress will show the wisdom to pass the bipartisan immigration bill by the end of the summer. They must, and I'm optimistic," he said Wednesday at a Washington dinner for the Asian Pacific American Institute for Congressional Studies.

"My optimism isn't based on any false notion," he continued. "It's based on my absolute firm belief that the American heart has changed, as well."

The Senate Judiciary Committee markup begins Thursday for comprehensive legislation proposed by a bipartisan group of eight senators, known as the Gang of Eight. The bill outlines a pathway to citizenship for most of the 11 million undocumented immigrants in the country, as well as tighter border security and better enforcement of current laws.

While the bill represents the most substantive legislation proposed on immigration reform since efforts were made-but ultimately failed-in 2007, the proposal has nonetheless seen strong pushback by some on the right.

The Heritage Foundation, a widely-known conservative think tank in Washington, released a report this week indicating the bill would cost $6.3 trillion in taxpayer dollars over the next 50 years and called for Congress to pass immigration laws in a piece-by-piece approach, rather than through an all-encompassing bill.

Republican Sen. Marco Rubio of Florida, part of the Gang of Eight, hit back against the report, saying he didn't consider it "legitimate."

Critics on the right have also taken issue with the bill's component that calls for a pathway to citizenship.

At the same time, Republicans seem to be more open to immigration reform than they were the last time around. Shortly after the GOP lost last year's presidential election, high-profile Republicans argued the party needed to make immigration a higher priority, given the low turnout among Latinos for Republican candidates. Mitt Romney won 27% of Latino voters, according to CNN exit polls.

More than two dozen conservative leaders signed a joint-statement released Thursday, pledging support for immigration reform and calling the current Senate bill an "important starting point."

"Simply opposing immigration reform should not be the conservative response to this problem. We believe conservatives should be leading the way on this issue by supporting legislation that upholds conservative principles," the statement read.

It was spearheaded by Al Cardenas, chairman of the American Conservative Union, and co-signed by prominent conservatives, including Faith and Freedom Coalition Chairman Ralph Reed, American Enterprise Institute scholar Paul Wolfowitz, American Action Forum Chairman Fred Malek, and Susan B. Antony List President Frank Cannon.

Biden, speaking earlier Wednesday at a State Department event on Western Hemisphere affairs, said working toward immigration reform is "granting (immigrants) the dignity and respect they deserve."

"It's hard to make the case in my view to 600 million people in the hemisphere that we genuinely respect you all but we do not show respect for 11 million people here in America, who hail from the very countries we talk about respecting," he said. "That's why we're absolutely committed to genuine immigration reform."