WASHINGTON (AP) — A bipartisan House group that’s been working in secret to write a comprehensive immigration bill splintered Friday with the departure of two Republicans, the latest sign of difficulty in solving the contentious issue.

Texas Reps. John Carter and Sam Johnson said they can no longer be part of the effort because they don’t trust President Barack Obama to enforce any legislation they write.

Their move may amount to the end of the group, which even before Friday’s development had failed to produce a final product after months of delay. Rep. Mario Diaz-Balart of Florida is now the sole Republican with four Democrats involved in the effort. Another Republican, Rep. Raul Labrador of Idaho, departed the group several months ago.

A joint statement from Johnson and Carter underscored how the thorny immigration issue is made even tougher by partisan politics on Capitol Hill and the distrust many House Republicans have for Obama.

“The administration’s practice of hand-picking what parts of laws they wish to enforce has irrevocably damaged our efforts of fixing our broken immigration system,” their statement said.

“If past actions are the best indicators of future behavior, we know that any measure depending on the president’s enforcement will not be faithfully executed. It would be gravely irresponsible to further empower this administration by granting them additional authority or discretion with a new immigration system,” they said. “The bottom line is — the American people do not trust the president to enforce laws, and we don’t either.

However, it’s not clear the development will have much of an impact on what the House does with respect to immigration, since House Republican leaders already had made clear they planned to proceed with a step-by-step approach, not with a single big bill like Johnson and Carter’s group had working on or like the Senate passed in June.

The group’s failure to deliver had already made it largely an afterthought in the House, where the Judiciary Committee has moved forward with individual, single-issue immigration bills that could come to the House floor sometime later this year or next. For now, immigration is on the back burner as Congress confronts pressing deadlines over the budget and federal debt.

The Senate bill, strongly backed by the White House, includes billions for border security, a reworked legal immigration system to allow tens of thousands of high- and low-skilled workers into the country, and a 13-year path to citizenship for the 11 million immigrants already here illegally. The bill being written by the House working group, which was said to be largely complete, proceeded along similar lines, although with a somewhat longer path to citizenship and other, tougher elements.

Most House Republicans reject this comprehensive approach and many question offering citizenship to people who broke U.S. immigration laws to be in this country. And although House Republican leaders say they want to solve the issue, which has become a political drag for the GOP, many rank-and-file House Republicans appear to have little desire to deal with it. So for now, it’s unclear whether the GOP-led House will ever pass legislation that could form the basis for a final deal with the Democratic-controlled Senate.

A Democratic member of the working group, Rep. Luis Gutierrez of Illinois, said that he and others who support immigration overhaul legislation would now turn their efforts to pressuring House Speaker John Boehner and other GOP leaders.

“It is clear the bipartisan group’s work was not being embraced by Republican leaders, so this allows us to put the focus squarely on Speaker Boehner and his lieutenants to decide if they are serious about reform and if so, to do something more than talk,” Gutierrez said in a statement.