Republicans have opened a series of public hearings around the US on the controversial issue of immigration.
Republicans want a bill focused on enforcing border security
Republicans in the House of Representatives are seeking approval for the House's tough immigration bill in a hearing in San Diego.
But Republican senators have set up their own session in Philadelphia to back a more liberal Senate proposal.
The issue has divided the party, with President George W Bush's vision initially closer to that of the Senate.
However, reports suggest the president is now moving closer to the conservative line.
The decision by Republican House leaders to call public hearings on the issue was seen by many as a serious setback for the president, who has been trying to see a bill passed ahead of mid-term elections in November.
The House and Senate have passed contrasting immigration bills, but work to reconcile the two bills is now delayed until the hearings are over.
Both bills seek to tighten border security, but while the Senate bill includes a guest-worker programme and offers illegal immigrants a "path to citizenship", the House's "enforcement-only" bill seeks to deport illegal immigrants and make it a felony to remain in the US illegally.
Democrats have dismissed the hearings as political theatre.
The first hearing took place on Wednesday at a San Diego Border Patrol station.
Republicans at the hearing highlighted the dangers of terrorists getting across the border.
HOUSE BILL VS SENATE BILL
HOUSE BILL (passed December)
Focuses on border security
Backs construction of fence along border with Mexico
Makes it a felony to live in the US illegally instead of a civil offence
Seeks to deport illegal immigrants
SENATE BILL (passed May)
Also toughens border security
Allows some illegal immigrants to seek US citizenship
Proposes guest-worker programme
"Immigration reform must be national security reform," said Ed Royce, a California Republican and chairman of the House's International Relations subcommittee on International Terrorism and Non-proliferation which is behind the hearings.
Another hearing will take place in Laredo, Texas on Friday, and reports suggest Arizona will also host one of the hearings.
Meanwhile, senators organised their own hearing in Philadelphia on Wednesday to defend the broad scope of the Senate immigration bill.
The hearing aimed to "develop a broader, factual, evidentiary record on the need for the comprehensive bill, which is challenged by quite a number of House members", said the host of the meeting, Pennsylvania Republican Sen Arlen Specter, ahead of the meeting.
But the New York Times newspaper has reported that President Bush, whose stance on immigration initially appeared to correspond more closely with the Senate bill, is moving closer to a compromise with conservatives on immigration.
Bush is said to be shifting his stance on immigration
It quoted Candi Wolff, White House director of legislative affairs, as saying Mr Bush is considering "triggers" on the immigration bill.
This refers to the idea that the guest-worker and "path to citizenship" schemes which Mr Bush has publicly backed could be introduced only once border-security targets have been met.
This "enforcement-first" approach would bring Mr Bush much closer to the "enforcement-only" measures demanded by his Republican colleagues in the House.