A comprehensive immigration overhaul bill is not expected until mid-April at the earliest, but four members of the Senate Gang of Eight - the team of bipartisan senators tasked with creating an immigration bill- will visit the Arizona-Mexico border today.

The two Arizona senators - both Republicans and Gang of Eight members, Sens. John McCain and Jeff Flake - will host Democrats Chuck Schumer of New York and Michael Bennet of Colorado for a tour along the border in Nogales, part of the Tucson sector. They will hold a news conference after the visit.

The visit comes in advance of the pending immigration legislation to bring 11 million undocumented on a possible path to citizenship.

At a Monday town hall meeting, McCain said the team has made progress in "a number of areas" that he is "encouraged" by, but there are still areas on which the team has been unable to come to agreements.

"I don't know if we can achieve agreement or not," he said. "We have been working, literally, night and day. We may not succeed."

The location for the tour, Nogales, sits in rural Arizona, a trouble spot on the border because of a funneling-effect resulting from tougher controls in cities like El Paso, Texas and San Diego, Calif.

"Right now in the street in Nogales you can probably buy a birth certificate for about fifty dollars," McCain said at Monday's town hall when speaking of the need for tamper-proof documents as a part of overhaul.

The Department of Homeland Security has focused on the region. The Tucson sector reported making the most apprehensions and the most drug seizures out of all nine border sectors in 2011, according to a Government Accountability Office report released in February